main:
	Read rows
	Read columns
	Read terrain
	Find the maximum perimeter
	If maximum perimeter is 0
		Print impossible
	Else
		Print maximum perimeter and its coordinates

Find the maximum perimeter:
	Create maximum perimeter as 0
	Create maximum coordinates as (0,0)-(0,0)
	Repeat concurrently|in parallel (ciclically) top left row for each row of terrain except last one
		Repeat top left column for each column of terrain except last one
			Create local perimeter as the result of finding maximum perimeter that can be formed from row and column
			Critic region:
				If local perimeter is larger than the maximum perimeter
					Assign maximum perimeter to the local perimeter
					Assign maximum coordinates to the local rectangle's coordinates

Find maximum perimeter that can be formed from (top left row, top left column):
	Create maximum perimeter as 0
	Create maximum coordinates as (0,0)-(0,0)
	Repeat bottom right row from top left row + 1 to the last one
		Repeat bottom right column from top left column + 1 to the last one
			If can form rectangle from top left cell to bottom right cell
				Create local perimeter as result of calculate perimeter
				If local perimeter is larger than the maximum perimeter
					Assign maximum perimeter to the local perimeter
					Assign maximum coordinates to the local rectangle's coordinates
	Return the maximum perimeter as a record of perimeter and coordinates

Can form rectangle from top left cell to bottom right cell:
	Repeat column from top left column to bottom right column
		If cell at top row is x or cell at bottom row is x then
			Return false
	Repeat row from top left row + 1 to bottom right row - 1
		If cell at left column is x or cell at right column is x then
			Return false
	Return true

Calculate perimeter:
	Return 2 * (bottom right column - top left column - 1) + 2 * (bottom right row - top left row - 1)