from collections import deque
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10 ** 7)

move = ((
    (1, 2), (1, -2), (-1, 2), (-1, -2),
    (2, 1), (2, -1), (-2, 1), (-2, -1)
), (
    (-1, -1), (1, 1), (1, -1), (-1, 1)
))

H, W = map(int, input().split())
G = [input().rstrip() for _ in range(H)]
for i in range(H):
    for j in range(W):
        if G[i][j] == "S":
            sx, sy = i, j
        if G[i][j] == "G":
            gx, gy = i, j

inf = 10**9
dist = [[[inf] * 2 for _ in range(W)] for _ in range(H)]
dist[sx][sy][0] = 0
que = deque([(sx, sy, 0)])
while que:
    x, y, f = que.popleft()
    d = dist[x][y][f]
    for dx, dy in move[f]:
        nx = x + dx
        ny = y + dy
        if 0 <= nx < H and 0 <= ny < W:
            nf = f
            if G[nx][ny] == "R":
                nf = f ^ 1
            if dist[nx][ny][nf] > d + 1:
                dist[nx][ny][nf] = d + 1
                que.append((nx, ny, nf))

ans = min(dist[gx][gy][0], dist[gx][gy][1])
if ans >= inf:
    ans = -1
print(ans)