# Lazy Caterer Sequence

Time Limit: 2 seconds

Memory Limit: 64 megabytes

## Description

Lazy caterer sequence is defined as the maximum number of pieces formed when slicing a convex pancake with n cuts (each cut is a straight line). The formula is Cn = n·(n + 1) / 2 + 1. You are given n; calculate n-th element of the sequence.

## Input

The only line of the input contains an integer n (0 ≤ n ≤ 100).

## Output

Output the n-th element of lazy caterer sequence.

## Sample Input

Input2Output4Input5Output16

## Sample Output

None

None

None