diff --git a/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/Dockerfile b/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/Dockerfile
new file mode 100644
index 0000000..381df27
--- /dev/null
+++ b/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/Dockerfile
@@ -0,0 +1,34 @@
+# Stage 1: Build
+FROM ubuntu:22.04 AS builder
+
+WORKDIR /app
+
+RUN set -xe; \
+    apt-get -yqq update; \
+    apt-get -yqq install build-essential \
+    ;
+
+COPY ./rwslotmachine4.c .
+COPY ./Makefile.sol ./Makefile
+
+RUN make
+
+# Stage 2: Runtime
+FROM ubuntu:22.04
+
+RUN set -xe; \
+     apt-get -yqq update;\
+     apt-get -yqq install libstdc++6; \
+     rm -rf /var/lib/apt/lists/* \
+;
+
+WORKDIR /app
+
+# Copy compiled binary from builder stage
+COPY --from=builder /app/rwslotmachine4 .
+
+# Expose port
+EXPOSE 31347
+
+# Run the executable
+CMD ["/app/rwslotmachine4"]
diff --git a/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/Makefile b/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/Makefile
new file mode 100644
index 0000000..0323ce0
--- /dev/null
+++ b/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/Makefile
@@ -0,0 +1,17 @@
+PORT ?= 31347
+IMG_NAME ?= rwslotmachine4
+CONT_NAME ?= $(IMG_NAME)-cnt
+
+build:
+	docker build -t $(IMG_NAME) -f Dockerfile .
+
+run: build
+	docker run -d --rm -p $(PORT):31337 --name $(CONT_NAME) -t $(IMG_NAME)
+
+stop:
+	-docker stop $(CONT_NAME)
+
+clean: stop
+	docker rm $(CONT_NAME)
+
+.PHONY: build run stop clean
diff --git a/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/Makefile.sol b/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/Makefile.sol
new file mode 100644
index 0000000..960783c
--- /dev/null
+++ b/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/Makefile.sol
@@ -0,0 +1,11 @@
+TARGET = rwslotmachine4
+
+all: $(TARGET)
+
+$(TARGET): rwslotmachine4.c
+	$(CC) -o $(TARGET) rwslotmachine4.c
+
+clean:
+	-rm -f $(TARGET)
+
+.PHONY: all clean
diff --git a/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/README.md b/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/README.md
new file mode 100644
index 0000000..ac5aa89
--- /dev/null
+++ b/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/README.md
@@ -0,0 +1,27 @@
+# Building and Running
+
+The included Makefile automates building and running the Docker container.
+
+- Build the Docker image:
+
+    ```bash
+    make build
+    ```
+
+- Run the container:
+
+    ```bash
+    make run
+    ```
+
+- Stop the running container:
+
+    ```bash
+    make stop
+    ```
+
+- Clean up container state:
+
+    ```bash
+    make clean
+    ```
diff --git a/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/rwslotmachine4.c b/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/rwslotmachine4.c
index 753493b..e71f1e1 100644
--- a/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/rwslotmachine4.c
+++ b/chapters/mitigations-and-defensive-strategies/defense-mechanisms/activities/04-rwslotmachine4/sol/rwslotmachine4.c
@@ -6,7 +6,18 @@
 
 #define MAX_SLOTS 32
 
-long read_int(int base);
+long read_int(int base)
+{
+	char buf[64];
+	char *endptr;
+
+	if (fgets(buf, sizeof(buf), stdin) == NULL) {
+		puts("Failed to read input!");
+		exit(1);
+	}
+
+	return strtol(buf, &endptr, base);
+}
 
 long slots[MAX_SLOTS];