303409: CF661A. Lazy Caterer Sequence

Memory Limit：64 MB Time Limit：2 S
Judge Style：Text Compare Creator：
Submit：0 Solved：0

Description

A. Lazy Caterer Sequencetime limit per test2 secondsmemory limit per test64 megabytesinputstandard inputoutputstandard output

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.

ExamplesInput
2
Output
4
Input
5
Output
16

Input

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