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