杭电ACM 1001

Sum Problem

Time Limit: 1000/500 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 406156    Accepted Submission(s): 102002

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

1100

 

Sample Output

1
5050
#include<iostream>using namespace std;int main(){    int a;    while(cin>>a){        if(0==a%2)///防止溢出          cout<<(a/2*(a+1))<<endl<<endl;        else          cout<<(a+1)/2*a<<endl<<endl;    }    return 0;}