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

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

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

  if(argc != 2){
    printf("Usage: recursive_factorial <NUMBER>\n");
    exit(1);
  }

  if(sscanf(argv[1], "%d", &n) == 0){
    printf("Error: %s is not a number.\n", argv[1]);
    exit(1);
  }

  if(n > 12){
    printf("Factorial of %d is too large for this program to calculate.\n", n);
    printf("Sorry.\n");
    exit(1);
  }
  printf("Factorial of %d is %d\n", n, factorial(n));

  return 0;
}