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## （hdoj1001）Sum Problem

By Wu Yudong on May 07, 2018

Problem - 1001

 Problem Description Hey, welcome to HDOJ(Hangzhou Dianzi University Online Judge). In this problem, your task is to calculate SUM(n) = 1 + 2 + 3 + ... + n. Input The input will consist of a series of integers n, one integer per line. Output For each case, output SUM(n) in one line, followed by a blank line. You may assume the result will be in the range of 32-bit signed integer. Sample Input 1 100 Sample Output 1 5050

#include<stdio.h>
#include<math.h>
#include<string.h>

int main()
{
long n;
while(scanf("%ld",&n)!=EOF)
printf("%ld\n\n", n%2? (n+1)/2*n: n/2*(n+1));
return 0;
}