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Nusrat's Treat

Limits: 1s, 512 MB

We all know how much Nusrat loves chocolate! She gets a lot of chocolate from her friends and family but she doesn’t share with anyone. But since you are a programmer and came to participate in this contest she will give you some chocolates on one condition. She, for some reason, always gives treat to junior programmers :P.

The condition is if you solve 1 problem you’ll get 1 chocolate. if you solve 2 problems you’ll get 3 chocolates. if you solve 3 problems you’ll get 6 chocolates and so on.

How many chocolates will you get if you solve N problems?

Input

The input will contain a single integer N (0 ≤ N ≤ 12).

Output

Print the number of chocolates you will get after solving N problems.

Samples

InputOutput
1
1
2
3
3
6

For the 2nd test case, you’ll get 1 + 2 = 3 chocolates.

For the 3rd test case, you’ll get 1 + 2 + 3 = 6 chocolates.

Discussion
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