Ural 1068 - Sum

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   Ninclusive.

Sample

input	output
-3	-5

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

// Ural Problem 1068. Sum

// Verdict: Accepted  

// Submission Date: 23:26:08 14 Jan 2014

// Run Time: 0.015s

//  

// 版权所有（C）acutus   (mail: [email protected]) 

// 博客地址：http://www.cnblogs.com/acutus/

// [解题方法]  

// 简单题，直接计算，注意N为负值



#include<stdio.h>



void solve()

{

    int N;

    scanf("%d", &N);

    if(N ==0) {

        printf("1\n");

        return;

    }

    if(N % 2) {

        printf("%d\n",(N > 0 ? ((N + 1)/2 * N) : (-1 * (-1 * N + 1)/2 * (-1 * N) + 1))); 

    } else {

        printf("%d\n", (N > 0 ? (N/2 * (N + 1)) : (-1 * (-1 * N)/2 * (-1 * N + 1) + 1)));

    }

}



int main()

{

    solve();

    return 0;

}