#include <iostream.h>
int main()
{ //  PRE: The user enters an integer >= 0 
  // POST: Shows the sum of the first n integers
  int j, n;
  int sum = 0;
  cout << "Enter n: ";
  cin >> n;
  for(j = 1; j <= n; j++)
  {
    sum = sum + j;
  }
  cout << "The sum of the first " << n << " integers is " << sum << endl;
  cout << "With  Gauss's  formula, the sum is " << (n*(n+1))/2 << endl;
  return 0;
}