#include<stdio.h>
void main()
{
    int a;
    long long factorial = 1;
    scanf("%d",&a);
    if(a< 0 || a< -20 || a>20)
    {
        printf("Invalid input\n");
    }
    else
    {
        for(int i = 1, i <=a;i++){
            factorial *=i;
        }
        print("%lld\n",factorial);
    }
    return 0;
}