Sum Problem

Sum Problem

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>

int main()

{

double n,sum=0;

while(scanf("%lf",&n)!=EOF)

    {

        sum=(1+n)/2*n;

        printf("%.0lf\n",sum);

        printf("\n");

    }

return 0;

}

 

输出格式注意有个空行。不要考虑得太复杂。。。