import heapq
H,W = map(int,input().split())
s = [input() for i in range(H)]
sx,sy,gx,gy = 0,0,0,0
for i in range(H):
	for j in range(W):
		if s[i][j] == 'S':
			sy = i
			sx = j
		elif s[i][j] == 'G':
			gy = i
			gx = j
used = [[[False for k in range(2)]for j in range(W)] for i in range(H)]
find = False
adx = [2,-2,2,-2,1,-1,1,-1]
ady = [1,1,-1,-1,2,2,-2,-2]
bdx = [1,1,-1,-1]
bdy = [1,-1,1,-1]
q = []
heapq.heappush(q,[0,sy,sx,True]) 
used[sy][sx][0] = True
while len(q) > 0 and (not find):
	hq = heapq.heappop(q)
	c = hq[0]
	y = hq[1]
	x = hq[2]
	isKnight = hq[3]
	cdy = bdy
	cdx = bdx
	if isKnight:
		cdy = ady
		cdx = adx
	for i in range(len(cdx)):
		ny = cdy[i] + y
		nx = cdx[i] + x
		mode = isKnight
		if ny < 0 or nx < 0 or ny >= H or nx >= W:continue
		if isKnight:
			if used[ny][nx][0]:continue
		else:
			if used[ny][nx][1]:continue
		if ny == gy and nx == gx:
			print(c + 1)
			find = True
			break
		if s[ny][nx] == 'R':
			mode = (not mode)
		if isKnight:
			used[ny][nx][0] = True
		else:
			used[ny][nx][1] = True
		heapq.heappush(q,[c + 1,ny,nx,mode])
if not find:
	print (-1)