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A. Lazy Caterer Sequence
time limit per test
2 seconds
memory limit per test
64 megabytes
input
standard input
output
standard 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.

Examples
Input
2
Output
4
Input
5
Output
16