#include<stdio.h>
int factorial(inti(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;
}