HDU-1001（Sum Problem）

Sum Problem

Time Limit: 1000/500 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)

Total Submission(s): 502707 Accepted Submission(s): 127610

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>

int main()
{
int n;
while(scanf("%d",&n)!=EOF)
{
printf("%.f\n\n",(1+n)/2.0*n);
}
return 0;
}