Problem 1001. -- Sum Problem

## HDU_1001: Sum Problem

Time Limit: 500 MS  Memory Limit: 32 MB   64bit IO Format: %I64d
Submitted: 681  Accepted: 263
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## 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

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