import Queue

H, W = map(int, raw_input().split())
field = [raw_input() for i in range(H)]

sx, sy, gx, gy = -1, -1, -1, -1
for i in range(H):
    for j in range(W):
        if field[i][j] == "S":
            sx = i
            sy = j
        if field[i][j] == "G":
            gx = i
            gy = j

inf = 99999999

d = [[[inf] * 2 for j in range(W)] for i in range(H)]
d[sx][sy][1] = 0
que = Queue.Queue()
que.put((sx, sy, 1))    # x, y, mode(1 = knight, 0 = mini-bishop)

while not que.empty():
    x, y, mode = que.get()
    if mode == 1:
        # knight
        dx = [2, 2, 1, 1, -1, -1, -2, -2];
        dy = [1, -1, 2, -2, 2, -2, 1, -1];
        for k in range(8):
            nx = x + dx[k]
            ny = y + dy[k]
            if not (0 <= nx < H and 0 <= ny < W):
                continue
            nxt_mode = mode ^ (field[nx][ny] == "R")
            if d[nx][ny][nxt_mode] == inf:
                d[nx][ny][nxt_mode] = d[x][y][mode] + 1
                que.put((nx, ny, nxt_mode))
    else:
        # mini-bishop
        dx = [1, 1, -1, -1]
        dy = [1, -1, 1, -1]
        for k in range(4):
            nx = x + dx[k]
            ny = y + dy[k]
            if not (0 <= nx < H and 0 <= ny < W):
                continue
            nxt_mode = mode ^ (field[nx][ny] == "R")
            if d[nx][ny][nxt_mode] == inf:
                d[nx][ny][nxt_mode] = d[x][y][mode] + 1
                que.put((nx, ny, nxt_mode))

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