#include <iostream>
#include <stdlib.h>

using namespace std;

/** Computes the factorial of the nonnegative integer n.
 * @pre n must be greater than or equal to 0.
 * @post None.
 * @return The factorial of n; n is unchanged. */
int fact(int n)
{
   if (n == 0)
      return 1;
   else
      return n * fact(n-1);
}

int main()
{
  int N, result;
  
  cout << "Enter a non-negative integer: ";
  cin >> N;
  if(N < 0){
    cout << N << " is a negative integer\n";
    exit(0);
  }

  result = fact(N);
  cout << "Factorial of " << N << " is " << result << endl;
  return 0;
}