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

 

Author

DOOM III

 

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这题其实没有想象的那么简单，要注意先除后乘这样不会爆掉，所以还要考虑奇偶，不过还有种办法是用double存，最后强转回int 也可以



#include<queue>

#include<math.h>

#include<stdio.h>

#include<string.h>

#include<iostream>

#include<algorithm>

using namespace std;

#define N 115





int main()

{

    int n;

    __int64 w;

    while(~scanf("%d",&n))

    {

        if(n%2==0) w=n/2*(n+1);

        else w=(n+1)/2*n;

        printf("%I64d\n\n",w);

    }









    return 0;

}

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