import sequtils,queues,strutils
proc R:any=stdin.readLine
var
 hw=R().split.map parseInt
 h=hw[0]
 w=hw[1]
 M=newSeqWith(h,R())
 s,g:tuple[x,y:int]
 q=initQueue[tuple[x,y,k,d:int]]()
 DP=newSeqWith(w,newSeqWith(h,[9999,9999]))
for y in 0..<h:(for x in 0..<w:(if M[y][x]=='S':s=(x,y);if M[y][x]=='G':g=(x,y)))
DP[s.x][s.y][0] = 0
q.enqueue (s.x,s.y,1,0)
while q.len > 0:
 let(x,y,k,f)=q.dequeue
 for d in [@[(1,1),(-1,-1),(1,-1),(-1,1)],@[(1,2),(2,1),(-1,-2),(-2,-1),(-1,2),(-2,1),(1,-2),(2,-1)]][k]:
  let(nx,ny)=(x+d[0],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 $(f+1),0
  let nk=if M[ny][nx]=='R':1-k else:k
  if DP[nx][ny][nk]<=f+1:continue
  DP[nx][ny][nk]=f+1
  q.enqueue (nx,ny,nk,f+1)
echo -1