A 8x8 chessboard is usually marked as follows: rows are marked by digits, 1 through 8, and columns are marked by letters, 'a' through 'h'. A cell is described by its column mark and then its row mark, like "e4".
While working on a chess program, you need to convert these descriptions into your internal cell numbers and back. Internally, cells are numbered row-by-row from 1 to 64 in your program, i.e., cell "a1" has number 1, cell "b1" has number 2, cell "c1" has number 3, ..., cell "h8" has number 64.
Given a String cell, describing either the cell mark or the cell number, change the notation (i.e., if you're given the mark you need to return the number, and vice versa).