#include <iostream>

using namespace std;

int main()
{
  int n; int sum;
  int savedN;

  sum = 0;
  cout << " Please input a positive integer " <<endl;
  cin >> n;
  savedN = n; //save n for later use

  while (n > 0)
  {
	  sum = sum + n;
	  n = n - 1;
	  cout << " n = " << n << " sum = " << sum << endl;

  }
  //ASSERT: n is 0 at this point sinec we decremented in the loop

  cout << " Sum of " << savedN << " natural number is "
       << sum << endl << endl << endl;

  cout << " Verification " << (savedN * (savedN + 1))/2 << endl;

  return 0;
}