Timus 1068

1068. Sum

Time limit: 2.0 second
Memory limit: 64 MB

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 a single integer number that is the sum of all integer numbers lying between 1 and N inclusive.

Sample

input	output
-3	-5

Problem Source: 2000-2001 ACM Northeastern European Regional Programming Contest (test tour)

#include<iostream>

#include<cstdio>

#include<cmath>

using namespace std;

int main()

{

    int n, sum;

    scanf("%d", &n);

    sum = 0;

    if(n>0)

    {

        sum = (n*(n+1))/2;

    }

    else if(n<=0)

    {

        sum = ((n*(n-1))/2)*(-1);

        sum = sum + 1;

    }

    printf("%d\n", sum);

}