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

int Fact( int n );

int main(int argc, char **argv)
{
    int n;
    if ( argc == 2 ) {
        n = atoi(argv[1]);
    } else {
        n = 1;
    }
    printf("Factorial of %d is %d.\n", n, Fact(n));
    return 0;
}

int Fact( int n )
{
    if ( n == 1 )
        return 1;
    else
        return n * Fact( n - 1 );
}