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A. Hexagonal Numbers

time limit per test

2 secondsmemory limit per test

256 megabytesinput

standard inputoutput

standard outputHexagonal numbers are figurate numbers which can be calculated using the formula *h*_{n} = 2*n*^{2} - *n*. You are given *n*; calculate *n*-th hexagonal number.

Input

The only line of input contains an integer *n* (1 ≤ *n* ≤ 100).

Output

Output the *n*-th hexagonal number.

Examples

Input

3

Output

15

Input

6

Output

66

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