Block Triangle

Background

Dawei is playing with blocks. He enjoys building various shapes with them, and one of his favorites is a triangle.

Problem Description

We have a 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.

Input Format

Input is given from Standard Input in the following format.

rows

Output Format

Output is printed to Standard Output in the following format.

total_blocks

Sample

0

0

1

1

2

3

Sample Explanation

For $0$ rows, there are $0$ blocks in total. For $1$ row, there is $1$ block in total. For $2$ rows, there are $1 + 2 = 3$ blocks in total.

Constraints

Time limit: $1$ second, Memory limit: $1024$ KiB for each test case.