Problem:
Factorial

Write a program which reads an integer n and prints the factorial of n. You can assume that n ≤ 20.

Input

An integer n (1 ≤ n ≤ 20) in a line.

Output

Print the factorial of n in a line.

Sample Input

5

Output for the Sample Input

120

Solution in C# (judge verdict: Accepted)

namespace AIDU {
    class AIDU0019
    {
        public static void Main(){
            ulong a=1;
            byte n=byte.Parse(System.Console.ReadLine());
            for(byte i=1;i<=n;i++) a*=i;
            System.Console.WriteLine(a);
        }
    }
}