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

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