ACM HDU1001Sum Problem

Sum Problem

Time Limit: 1000/500 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 113869    Accepted Submission(s): 26069

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

 

Author

DOOM III

 

 

#include<stdio.h>
int main()
{
    int n;
    int sum;
    while(scanf("%d",&n)!=EOF)
    {
         if(n%2==0)  sum=n/2*(n+1);
         else sum=(n+1)/2*n;//防溢出 
         printf("%d\n\n",sum);
    }    
    return 0;
}