Problem DA: 编程求解1+2+3+...+n

Problem DA: 编程求解1+2+3+...+n

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Time Limit : 1.000 sec  Memory Limit : 128 MB

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Solved: 483Submit Num: 817Statistics

Description

编程求解下列式子的值：S=1+2+3+...+n

Input

输入一行，只有一个整数n

Output

输出整数S，S=1+2+3+...+n

Sample Input Copy 

100

Sample Output Copy 

5050
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