DIRS=[
	[[1,2],[2,1],[-1,2],[2,-1],[1,-2],[-2,1],[-1,-2],[-2,-1]],
	[[1,1],[-1,1],[1,-1],[-1,-1]]
]
h,w=gets.split.map(&:to_i)
rh=0...h
rw=0...w
board=h.times.map{gets.chomp}
sx=sy=tx=ty=0
h.times{|i|w.times{|j|
	if board[i][j]==?S
		sx=i
		sy=j
	elsif board[i][j]==?G
		tx=i
		ty=j
	end
}}

q=[]
s=[sx,sy,0]
q.push s
visited={}
visited[s]=0
t1=[tx,ty,0]
t2=[tx,ty,1]
until q.empty?||visited[t1]||visited[t2]
	state=q.shift
	x,y,piece=state
	step=visited[state]
	DIRS[piece].each{|dx,dy|
		nx=x+dx
		ny=y+dy
		next unless rh===nx&&rw===ny
		np=board[nx][ny]==?R ? 1-piece : piece
		next_state=[nx,ny,np]
		next if visited[next_state]
		visited[next_state]=step+1
		q.push next_state
	}
end

puts visited[t1]||visited[t2]||-1