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; }