#include <stdio.h>
int factorial(int n) {
    if (n == 0 || n == 1)
        return 1;
    else
        return n * factorial(n - 1);
}

int main() {
    int n;
    scanf("%d", &n);
    
    if (n < 0)  {
        printf("Invalid Input");
     }   else {
            print("%d", factorial(n));
        }
        
        return 0;
}