from collections import deque

H,W=map(int,input().split())
S=[input().strip() for i in range(H)]

DIS=[[1<<60]*W for i in range(H)]
DIS2=[[1<<60]*W for i in range(H)]

for i in range(H):
    for j in range(W):
        if S[i][j]=="S":
            Q=deque([(i,j,0)])
            DIS[i][j]=0

while Q:
    x,y,com=Q.popleft()

    if com==0:
        for z,w in [(x+1,y-2),(x+1,y+2),(x-1,y-2),(x-1,y+2),(x+2,y-1),(x+2,y+1),(x-2,y-1),(x-2,y+1)]:
            if 0<=z<H and 0<=w<W:
                if S[z][w]=="R":
                    if DIS2[z][w]>DIS[x][y]+1:
                        DIS2[z][w]=DIS[x][y]+1
                        Q.append((z,w,1))
                else:
                    if DIS[z][w]>DIS[x][y]+1:
                        DIS[z][w]=DIS[x][y]+1
                        Q.append((z,w,0))

    else:
        for z,w in [(x+1,y+1),(x+1,y-1),(x-1,y+1),(x-1,y-1)]:
            if 0<=z<H and 0<=w<W:
                if S[z][w]=="R":
                    if DIS[z][w]>DIS2[x][y]+1:
                        DIS[z][w]=DIS2[x][y]+1
                        Q.append((z,w,0))
                else:
                    if DIS2[z][w]>DIS2[x][y]+1:
                        DIS2[z][w]=DIS2[x][y]+1
                        Q.append((z,w,1))

ANS=1<<60

for i in range(H):
    for j in range(W):
        if S[i][j]=="G":
            ANS=min(ANS,DIS[i][j],DIS2[i][j])

if ANS==1<<60:
    print(-1)
else:
    print(ANS)