#include <stdio.h>
    double n;
    scanf("%1f", &n);
    
    if (n < -100 || n > 100 || n != (int)n) {
        printf("Invalid input");
        return 0;
    }
    int num = (int)n;
    if (num < 0){
        printf("Invalid input");
        return 0;
    }
    unsigned long long fact = 1;
    for (int i = 1; i <= num; i++){
        fact *= i;
    }
    printf("%llu", fact);
    return 0;
}