## page was renamed from 程序设计练习07——timus1068——Sum
= Sum =
http://acm.timus.ru/problem.aspx?space=1&num=1068

Time Limit: 2.0 second 

Memory Limit: 1 000 K

Your task is to find the sum of all integer numbers lying between 1 and N inclusive.

== Input ==
The input consists of a single integer N that is not greater than 10000 by it's absolute value.

== Output ==
Write to the output file a single integer number that is the sum of all integer numbers lying between 1 and N inclusive.

== Sample Input ==
{{{-3
}}}

== Sample Output ==
{{{-5
}}}



------
{{{#!cplusplus
#include <iostream>
using namespace std;

int main()
{
  int n;
  cin >> n;
  if(n>0) {
    cout << n*(n+1)/2 << endl;
  } else {
    cout << n*(-n+1)/2+1 << endl;
  }
}
}}}