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

Input
2
Output
4
Input
5
Output
16

Sample Output

None

Hint

None

Source

None

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