/* =========================================

   Filename:  sum_loop.c
   Filedate:  January 18, 2007

   The program asks for  positive integer  n 
   and then computes the following sum:

     2 + 3 + 6 + ... + (n*n - 2*n + 3)
   
   The computation uses a loop.

   =========================================  */

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

int main() {

  int i,n;
  int answer = 0;

  printf("\nInput a positive integer n.\n\n");
  scanf("%d", &n);

  for (i = 1; i <= n; i++) {
    answer = answer + i*i - 2*i + 3;
  }

  printf("\nWhen  n = %d,\n\n", n);
  printf("2 + 3 + 6 + ... + n*n - 2*n + 3 \n\n");
  printf("is:  %d\n", answer);
  return(0);
}