import sequtils,queues
type Pos = tuple[x,y:int]


proc getchar_unlocked():char {. importc:"getchar_unlocked",header: "<stdio.h>" .}
proc scan(): int =
  while true:
    let k = getchar_unlocked()
    if k < '0': return
    result = 10 * result + k.ord - '0'.ord

let h = scan()
let w = scan()
var M = newSeqWith(w,newSeq[bool](h)) # R かどうか
var s : Pos
var g : Pos
for y in 0..<h:
  for x in 0..<w:
    let k = getchar_unlocked()
    if k == 'S' : s = (x,y)
    if k == 'G' : g = (x,y)
    M[x][y] = k == 'R'
  discard getchar_unlocked()
const INF = 1e10.int
var DP = newSeqWith(w,newSeqWith(h,newSeqWith(2,INF))) # Pid Kni
DP[s.x][s.y][0] = 0
var q = initQueue[tuple[x,y,isKnight,d:int]]()
q.enqueue((s.x,s.y,1,0))
while q.len > 0:
  let (x,y,isKnight,diff) = q.dequeue()
  const D : seq[seq[Pos]] = @[
    @[(1,1),(-1,-1),(1,-1),(-1,1)],
    @[(1,2),(2,1),(-1,-2),(-2,-1),(-1,2),(-2,1),(1,-2),(2,-1)],
  ]
  let nextDiff = diff + 1
  for d in D[isKnight]:
    let nx = x + d[0]
    let ny = y + d[1]
    if nx < 0 or ny < 0 or nx >= w or ny >= h : continue
    if nx == g.x and ny == g.y : quit $nextDiff,0
    let nextIsKnight = if M[nx][ny]: 1 - isKnight else: isKnight
    if DP[nx][ny][nextIsKnight] <= nextDiff: continue
    DP[nx][ny][nextIsKnight] = nextDiff
    q.enqueue((nx,ny,nextIsKnight,nextDiff))
echo -1