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