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