#include<stdio.h>

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

int main(int argc, char **argv)
{
   if (argc > 1) {
      int n = atoi(argv[1]);
      printf("The factorial of %d is %d\n", n, fact(n));
      return 0;
   }
   else {
      puts("Please specify a number.");
      return -1;
   }
}