Hexagon with side \textbf{n} is divided into \textbf{6n^2} equilateral triangles with side \textbf{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.) \InputFile In the input file contains the number \textbf{n} (\textbf{1} ≤ \textbf{n} ≤ \textbf{7}). \OutputFile Display the number of tilings of a hexagon.