Hexagon and rhombic domino#1865

Hexagon and rhombic domino

1 second

256 megabytes

Easy

A hexagon with side $n$ is divided into $6 n^{2}$ 6n^2 equilateral triangles with side $1$ .

In how many ways can it be covered by rhombic dominoes (without overlaps and without going beyond the border)?

(A rhombic domino consists of two equilateral triangles with side $1$ , joined by an edge.)

Input

The input file contains the number $n$ ( $1 \leq n \leq 7$ 1 \leq n \leq 7).

Print the number of ways to tile the hexagon.

Example 1

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6 n^{2}

1 \leq n \leq 7