import sys
from collections import deque
sys.setrecursionlimit(10**7)
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def LI2(): return list(map(int,sys.stdin.readline().rstrip()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
def LS2(): return list(sys.stdin.readline().rstrip())


H,W = MI()
A = [S() for _ in range(H)]

for i in range(H):
    for j in range(W):
        if A[i][j] == 'S':
            si,sj = i,j
        if A[i][j] == 'G':
            gi,gj = i,j

directions_K = [(-2,-1),(-2,1),(-1,-2),(-1,2),(2,-1),(2,1),(1,-2),(1,2)]
directions_B = [(-1,-1),(-1,1),(1,-1),(1,1)]

dist = [[[-1]*W for _ in range(H)] for _ in range(2)]
dist[0][si][sj] = 0
deq = deque([(0,si,sj)])
while deq:
    k,i,j = deq.pop()
    if k == 0:
        for di,dj in directions_K:
            ni,nj = i+di,j+dj
            if 0 <= ni < H and 0 <= nj < W:
                if A[ni][nj] == 'R' and dist[1][ni][nj] == -1:
                    dist[1][ni][nj] = dist[k][i][j]+1
                    deq.appendleft((1,ni,nj))
                if A[ni][nj] != 'R' and dist[0][ni][nj] == -1:
                    dist[0][ni][nj] = dist[k][i][j]+1
                    deq.appendleft((0,ni,nj))
    else:
        for di,dj in directions_B:
            ni,nj = i+di,j+dj
            if 0 <= ni < H and 0 <= nj < W:
                if A[ni][nj] == 'R' and dist[0][ni][nj] == -1:
                    dist[0][ni][nj] = dist[k][i][j]+1
                    deq.appendleft((0,ni,nj))
                if A[ni][nj] != 'R' and dist[1][ni][nj] == -1:
                    dist[1][ni][nj] = dist[k][i][j]+1
                    deq.appendleft((1,ni,nj))

ans0,ans1 = dist[0][gi][gj],dist[1][gi][gj]
if ans0 == -1:
    if ans1 == -1:
        print(-1)
    else:
        print(ans1)
else:
    if ans1 == -1:
        print(ans0)
    else:
        print(min(ans0,ans1))