lets imagine a cat, standing on an infinitely long row of tiles. since its a 'cat', string length=3; it takes 3 tiles to stand.
Imagine the row of tiles marked as a continuous set of a-z. so the cat is standing in tiles marked as 'abc'.
Now, whenever the cat makes a call, it jumps the distance equal to the length of the call. e.g. if the call is 'meaw', length=4; it'll jump 4 tiles; placing itself in tiles 'hij'.
the output should contain the tiles before & after cat's current position. i.e. 'gk'.
n.b. initially the cat is in 'abc' >> so the output should contain only 'd' -- since there are no tiles before the 1st tile.