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A. Lazy Caterer Sequence

time limit per test

2 secondsmemory limit per test

64 megabytesinput

standard inputoutput

standard outputLazy 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 *C*_{n} = *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.

Examples

Input

2

Output

4

Input

5

Output

16

Codeforces (c) Copyright 2010-2019 Mike Mirzayanov

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