Hexagon with side n is divided into 6n^2 equilateral triangles with side 1.
In how many ways it can be covered by rhombic dominoes (without overlaps and goes beyond the border)?
(Orthorhombic domino consists of two equilateral triangles of side 1, adjacent to the side.)
In the input file contains the number n (1 ≤ n ≤ 7).
Display the number of tilings of a hexagon.