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John got a bad mark in math. The teacher gave him another task. John is to write a program which computes the sum of integers from 1 to . If he manages to present a correct program, the bad mark will be cancelled.

Write a program which:

- reads the number from the standard input,
- computes the sum of integers from 1 to ,
- writes the answer to the standard output.

The first and only line of the standard input contains one integer ().

One integer is to be written to the standard output. This integer should be the sum of integers from 1 to .

For the input data:

3

the correct result is:

6

*Task author: Piotr Stanczyk.*