#include <iostream>

using namespace std;

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


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

   if(argc!=2) {
      cerr << "Usage: " << argv[0] << " n" << endl;
      exit(EXIT_FAILURE);
   }

   int x = atoi(argv[1]);
   cout << "factorial(" << x << "): " << factorial(x) << endl;
   
   return EXIT_FAILURE;
}