diff --git a/C#/20.Factorial Digit Sum/frangiz.cs b/C#/20.Factorial Digit Sum/frangiz.cs
new file mode 100644
index 0000000..b99ce64
--- /dev/null
+++ b/C#/20.Factorial Digit Sum/frangiz.cs	
@@ -0,0 +1,32 @@
+using System;
+using System.Numerics;
+using System.Linq;
+
+namespace FactorialDigitSum
+{
+    public class MainClass
+    {
+        public static void Main()
+        {
+            BigInteger number = factorial(new BigInteger(100));
+
+            int ans = 0;
+            foreach (char c in number.ToString())
+            {
+                ans += c - '0';
+            }
+            Console.WriteLine(ans);
+        }
+
+        private static BigInteger factorial(BigInteger n)
+        {
+            BigInteger res = new BigInteger(1);
+            while (n > 1)
+            {
+                res *= n;
+                n -= 1;
+            }
+            return res;
+        }
+    }
+}
\ No newline at end of file
diff --git a/README.md b/README.md
index b794d72..bb95dcf 100644
--- a/README.md
+++ b/README.md
@@ -49,7 +49,7 @@ Happy Contributing! 😃
 | 17 | [Number letter counts](https://projecteuler.net/problem=17)                  |                    |                    |                    | :white_check_mark: |                    |                    |                    |                    |                    |                    |                    |                    |
 | 18 | [Maximum path sum I](https://projecteuler.net/problem=18)                    |                    |                    |                    | :white_check_mark: |                    |                    |                    |                    |                    |                    |                    |                    |
 | 19 | [Counting Sundays](https://projecteuler.net/problem=19)                      |                    |                    |                    |                    |                    |                    |                    |                    |                    |                    |                    |                    |
-| 20 | [Factorial digit sum](https://projecteuler.net/problem=20)                   |                    | :white_check_mark: |                    | :white_check_mark: | :white_check_mark: |                    |                    |                    |                    |                    |                    |                    |
+| 20 | [Factorial digit sum](https://projecteuler.net/problem=20)                   |                    | :white_check_mark: |                    | :white_check_mark: | :white_check_mark: |                    |                    | :white_check_mark: |                    |                    |                    |                    |
 | 21 | [Amicable numbers](https://projecteuler.net/problem=21)                      |                    |                    |                    |                    |                    |                    |                    |                    |                    |                    |                    |                    |
 | 22 | [Names scores](https://projecteuler.net/problem=22)                          |                    |                    |                    | :white_check_mark: |                    |                    |                    |                    |                    |                    |                    |                    |
 | 23 | [Non-abundant sums](https://projecteuler.net/problem=23)                     |                    |                    |                    |                    |                    |                    |                    |                    |                    |                    |                    |                    |