import sequtils,queues,times#,nimprof
type Pos = tuple[x,y:int16]
template stopwatch(body) = (let t1 = cpuTime();body;echo "TIME:",(cpuTime() - t1) * 1000,"ms")
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 : array[500,array[500,bool]]
const INF = int16.high
var DP : array[500,array[500,array[2,int16]]]
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.int16,y.int16)
    elif k == 'G' : g = (x.int16,y.int16)
    M[x][y] = k == 'R'
  discard getchar_unlocked()
DP[s.x][s.y][0] = -INF
var q = initQueue[tuple[x,y,isKnight,d:int16]]()
q.enqueue((s.x,s.y,1.int16,-INF))
let 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)],
].mapIt(it.mapIt((it[0].int16,it[1].int16)))
block:
  proc solve() : bool  =
    while q.len > 0:
      let (x,y,isKnight,diff) = q.dequeue()
      let nextDiff = diff + 1
      for i in 0..<(4 + isKnight * 4):
        let nx = x + D[isKnight][i].x
        let ny = y + D[isKnight][i].y
        if nx < 0 or ny < 0 or nx >= w or ny >= h : continue
        if nx == g.x and ny == g.y :
          echo nextDiff + INF
          return true
        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))
    return false
  if not solve(): echo -1