Background

Description

We have triangle made of blocks. The topmost row has 1 block, the next row down has 2 blocks, the next row has 3 blocks, and so on. Compute recursively (no loops or multiplication) the total number of blocks in such a triangle with the given number of rows.

Format

Input

Output

Samples

0

0

1

1

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Limitation

1s, 1024KiB for each test case.