hdu1001 Sum Problem （等差数列求和）

Sum Problem

Time Limit: 1000/500 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 334405    Accepted Submission(s): 84083

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

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解析：等差数列求和：Sn=（a1+an）*n/2。

代码：

#include<cstdio>
using namespace std;

int main()
{
  long long n;
  while(scanf("%I64d",&n)!=EOF)
    printf("%I64d\n\n",(n+1)*n/2);
  return 0;  
}