#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
    printf("%d", factorial(n));
    return 0;
}