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

int factorial(int x);

int main(int argc, char** argv) {
  if (argc != 2) {
    printf("Error requires exactly one argument\n");
    exit(1);
  }
  // Convert string to int
  int input = atoi(argv[1]);
  int output = factorial(input);
  printf("%d factorial is %d\n", input, output);
}

int factorial(int x) {
  if (x == 0) {
    return x;
  } else {
    return x * factorial(x-1);
  }
}