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