Problem F: 阶梯累加计算

Problem F: 阶梯累加计算

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Time Limit : 1.000 sec  Memory Limit : 128 MiB

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Description

输入整数x,y,求x+（x+1）+（x+2）+...+y的总和

例如：

3 7

就是3+4+5+6+7

Sample Input Copy 

3 7

Sample Output Copy 

25
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