// editor3
#include <stdio.h>
int main()
{
    int n,i;
   unsigned long long factorial=1;
    scanf("%d",&n);
    if(-20<n>20)
    {
        printf("Invalid Input\n");
        return 0;
    }
    if()
    else{
        for(int i=1;i<=n;++i)
       { factorial *=i;
       }
    printf("%lld\n",factorial);
    }
    return 0;
}