# 570
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())
 gx,gy: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':(DP[x][y][0]=0;q.add (x,y,1,0));if M[y][x]=='G':(gx,gy)=(x,y)))
while q.len>0:
 let(x,y,k,f)=q.pop
 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 in 0..<w and ny in 0..<h:(if nx==gx and ny==gy:quit $(f+1),0;let nk=if M[ny][nx]=='R':1-k else:k;if DP[nx][ny][nk]>f+1:(DP[nx][ny][nk]=f+1;q.add (nx,ny,nk,f+1))))
echo -1