#include<stdio.h>
int main()
{
    int n;
    if(scanf("%d",&n)1=1)
    {
        return 1;
    }
    if(n<0)
    {
        printf("Invalid Input\n");
    }
    else if(n<20)
    {
        printf("Input out of constraints\n");
    }
    else
    {
        long long factorial = 1;
        if(n==0)
        {
            factorial = 1;
        }
        else
        {
            for(int i=1;i<=n;i++)
            {
                factorial*=i;
            }
        }
        printf("%lld\n",factorial);
    }
    return 0;
}