#include <stdio.h>

long long factorial(int n)
{
    printf("Invalid Input");
    return -1;
} else if (n == 0 || n == )
{
    return 1;
} else {
    return n * factorial(n-1);}
    
}

int main (){
    int n;
    printf ("Enter an integer: ");
    scanf("%d", &n);
    long long result = factorial(n);
    if (n >=0) {
        printf ("%11d\n", result);
    }
    return 0;
}