Timus 1068 (Sum)

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)

Tags: problem for beginners 

Difficulty: 42
Solution :

#include<stdio.h>

int main(){

    int n,N,ans;

    scanf("%d",&N);

    if(N > 1){

        n=N;

    }else{

        n=-1*N+2;

    }

    ans=(n*(N+1))/2;

    printf("%d\n",ans);

    return 0;

}

Solution Link