diff --git a/task01/src/com/example/task01/Task01Main.java b/task01/src/com/example/task01/Task01Main.java
index de4599c1..25fa0f20 100644
--- a/task01/src/com/example/task01/Task01Main.java
+++ b/task01/src/com/example/task01/Task01Main.java
@@ -23,7 +23,11 @@ public static <T, U> Function<T, U> ternaryOperator(
             Function<? super T, ? extends U> ifTrue,
             Function<? super T, ? extends U> ifFalse) {
 
-        return null; // your implementation here
+        if (condition == null || ifTrue == null || ifFalse == null) {
+            throw new NullPointerException();
+        }
+
+        return t -> condition.test(t) ? ifTrue.apply(t) : ifFalse.apply(t);
 
     }
 }
diff --git a/task02/src/com/example/task02/Task02Main.java b/task02/src/com/example/task02/Task02Main.java
index 309260d8..ea63d69c 100644
--- a/task02/src/com/example/task02/Task02Main.java
+++ b/task02/src/com/example/task02/Task02Main.java
@@ -16,8 +16,13 @@ public static void main(String[] args) {
 
     public static IntStream cycleGrayCode(int n) {
 
-        return null; // your implementation here
+        if (n < 1 || n > 16) throw new IllegalArgumentException();
+        return IntStream.iterate(0, i -> i + 1).map(i -> grayCodeFromBinary(i % (int) Math.pow(2, n)));
 
     }
 
+    public static int grayCodeFromBinary(int g) {
+        return g ^ (g >> 1);
+    }
+
 }
diff --git a/task03/src/com/example/task03/Task03Main.java b/task03/src/com/example/task03/Task03Main.java
index 254d5cb0..ab36e755 100644
--- a/task03/src/com/example/task03/Task03Main.java
+++ b/task03/src/com/example/task03/Task03Main.java
@@ -1,6 +1,7 @@
 package com.example.task03;
 
 import java.util.Comparator;
+import java.util.Iterator;
 import java.util.function.BiConsumer;
 import java.util.stream.Stream;
 
@@ -22,6 +23,28 @@ public static <T> void findMinMax(
             Comparator<? super T> order,
             BiConsumer<? super T, ? super T> minMaxConsumer) {
 
-        // your implementation here
+        if (stream == null || order == null || minMaxConsumer == null) {
+            throw new NullPointerException();
+        }
+
+        Iterator<? extends T> iterator = stream.iterator();
+
+        if (!iterator.hasNext()) {
+            minMaxConsumer.accept(null, null);
+        } else {
+            T min = iterator.next();
+            T max = min;
+
+            while (iterator.hasNext()) {
+                T current = iterator.next();
+                if (order.compare(current, min) < 0) {
+                    min = current;
+                } else if (order.compare(current, max) > 0) {
+                    max = current;
+                }
+            }
+
+            minMaxConsumer.accept(min, max);
+        }
     }
 }
diff --git a/task04/src/com/example/task04/Task04Main.java b/task04/src/com/example/task04/Task04Main.java
index 1e38e6eb..cbb182d9 100644
--- a/task04/src/com/example/task04/Task04Main.java
+++ b/task04/src/com/example/task04/Task04Main.java
@@ -1,11 +1,28 @@
 package com.example.task04;
 
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.util.Comparator;
+import java.util.Map;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
 public class Task04Main {
 
     public static void main(String[] args) {
-
-        // your implementation here
-
+        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
+        reader.lines()
+                .flatMap(x -> Stream.of(x.split("\\P{L}"))
+                        .filter(t -> !t.isEmpty())
+                        .map(String::toLowerCase))
+                .collect(Collectors.groupingBy(t -> t, Collectors.counting()))
+                .entrySet()
+                .stream()
+                .sorted(Map.Entry.comparingByKey())
+                .sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
+                .limit(10)
+                .map(Map.Entry::getKey)
+                .forEach(t -> System.out.print(t + '\n'));
     }
 
 }
diff --git a/task05/src/com/example/task05/MailMessage.java b/task05/src/com/example/task05/MailMessage.java
new file mode 100644
index 00000000..7070d6a9
--- /dev/null
+++ b/task05/src/com/example/task05/MailMessage.java
@@ -0,0 +1,25 @@
+package com.example.task05;
+
+public class MailMessage implements Message<String> {
+    private String from;
+    private String to;
+    private String content;
+
+    public MailMessage(String from, String to, String content) {
+        this.from = from;
+        this.to = to;
+        this.content = content;
+    }
+
+    public String getFrom() {
+        return from;
+    }
+
+    public String getTo() {
+        return to;
+    }
+
+    public String getContent() {
+        return content;
+    }
+}
\ No newline at end of file
diff --git a/task05/src/com/example/task05/MailService.java b/task05/src/com/example/task05/MailService.java
new file mode 100644
index 00000000..f601499d
--- /dev/null
+++ b/task05/src/com/example/task05/MailService.java
@@ -0,0 +1,35 @@
+package com.example.task05;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.function.Consumer;
+
+public class MailService<T> implements Consumer<Message<T>> {
+    HashMap<String, List<T>> mailBox = new HashMap<String, List<T>>() {
+
+        @Override
+        public List<T> get(Object key) {
+            return super.get(key) == null ? new ArrayList<>() : super.get(key);
+        }
+    };
+
+    public MailService() {
+
+    }
+
+    public HashMap<String, List<T>> getMailBox() {
+        return mailBox;
+    }
+
+    @Override
+    public void accept(Message<T> message) {
+        if (!mailBox.containsKey(message.getTo())) {
+            mailBox.put(message.getTo(), new ArrayList<>());
+            mailBox.get(message.getTo()).add(message.getContent());
+        } else {
+            mailBox.get(message.getTo()).add(message.getContent());
+        }
+    }
+
+}
diff --git a/task05/src/com/example/task05/Message.java b/task05/src/com/example/task05/Message.java
new file mode 100644
index 00000000..85b845d8
--- /dev/null
+++ b/task05/src/com/example/task05/Message.java
@@ -0,0 +1,9 @@
+package com.example.task05;
+
+public interface Message<T> {
+    String getFrom();
+
+    String getTo();
+
+    T getContent();
+}
\ No newline at end of file
diff --git a/task05/src/com/example/task05/Salary.java b/task05/src/com/example/task05/Salary.java
new file mode 100644
index 00000000..0bea5789
--- /dev/null
+++ b/task05/src/com/example/task05/Salary.java
@@ -0,0 +1,28 @@
+package com.example.task05;
+
+public class Salary implements Message<Integer> {
+    private String from;
+    private String to;
+    private Integer content;
+
+    public Salary(String from, String to, Integer content) {
+        this.from = from;
+        this.to = to;
+        this.content = content;
+    }
+
+    @Override
+    public String getFrom() {
+        return from;
+    }
+
+    @Override
+    public String getTo() {
+        return to;
+    }
+
+    @Override
+    public Integer getContent() {
+        return content;
+    }
+}
\ No newline at end of file