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