H,W=map(int,raw_input().split())
B=[raw_input() for i in range(H)]
arrived=[[[-1 for i in range(2)] for j in range(W)] for k in range(H)]
state=[]
for i in range(H):
    for j in range(W):
        if B[i][j]=='S':
            state.append((0,0,i,j))
            arrived[i][j][0]=0
    
moves=[[(1,2),(2,1),(2,-1),(1,-2),(-1,-2),(-2,-1),(-2,1),(-1,2)],[(1,1),(-1,1),(-1,-1),(1,-1)]]

#cnt=0
while len(state)!=0:
    #print "now",cnt,":",len(state)
    nextState=[]
    for (p,s,x,y) in state:
        if B[x][y]=='G':
            print p
            exit()
        for (dx,dy) in moves[s]:
            nx,ny=x+dx,y+dy
            if nx<0 or ny <0 or nx>=H or ny >= W:
                continue
            ns=s
            if B[nx][ny]=='R':
                ns=1-s
            if arrived[nx][ny][ns]!=-1:
                continue
            arrived[nx][ny][ns]=p+1
            nextState.append((p+1,ns,nx,ny))
    state=nextState
#    cnt+=1
print -1