from collections import deque

h, w = map(int, input().split())
S = [list(input()) for _ in range(h)]

for i in range(h):
    for j in range(w):
        if S[i][j] == 'S':
            si, sj = i, j
        elif S[i][j] == 'G':
            gi, gj = i, j
INF = 10**18
DP = [[[INF for _ in range(2)] for _ in range(w)] for _ in range(h)]
DP[si][sj][0] = 0
Directions = [[(1, 2), (2, 1), (2, -1), (1, -2), (-1, -2), (-2, -1), (-2, 1), (-1, 2)],
              [(1, 1), (1, -1), (-1, -1), (-1, 1)]]
Que = deque([(si, sj, 0)])
while Que:
    ci, cj, idx = Que.popleft()
    if ci == gi and cj == gj:
        break
    cc = DP[ci][cj][idx]
    for di, dj in Directions[idx]:
        ni, nj = ci + di, cj + dj
        if 0 <= ni < h and 0 <= nj < w:
            if S[ni][nj] == 'R':
                nidx = idx ^ 1
            else:
                nidx = idx
            if cc + 1 >= DP[ni][nj][nidx]:
                continue
            DP[ni][nj][nidx] = cc + 1
            Que.append((ni, nj, nidx))

if min(DP[gi][gj]) == INF:
    print(-1)
else:
    print(min(DP[gi][gj]))