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

代码如下：

#include<stdio.h>

int main()

{   

 int n,m;   

 while(scanf("%d",&n)!=EOF)   

 {       

  if(n%2==0)            

  　　m=n/2*(n+1);        

  else            

  　　m=(n+1)/2*n;       

  printf("%d\n\n",sum);  

 }   

 return 0;

}

之前我没考虑奇偶问题，一直过不了。