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