#include <stdio.h>
#include <stdlib.h>

int factorial (int n);

int main (int argc, char **argv)
{
    int n;

    if (argc < 2) {
        printf ("Usage: %s n\n", argv [0]);
        return -1;
    }
    else {
        n = atoi (argv[1]);
        printf ("Factorial of %d is %d.\n", n, factorial (n));
    }

    return 0;
}