PROGRAMMING:Finding the cumulative sum of 1 to n

Enter an integer n and find the cumulative sum of 1 + 2 + 3 +... + n.
###Input format:
Enter an integer.
###Output format:
Output the cumulative sum of 1 ~ n.
###Input example:
```in
Here is a set of inputs. For example:
five
```
###Output example:
```out
The corresponding output is given here. For example:
fifteen
```






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