# Practice on Toph

Participate in exhilarating programming contests, solve unique algorithm and data structure challenges and be a part of an awesome community.

## Nusrat's Treat

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

Input | Output |
---|---|

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.