from collections import deque


def list3(a, b, c, *, val=0):
    return [[[val] * c for _ in range(b)] for _ in range(a)]


H, W = map(int, input().split())
G = [input() for _ in range(H)]


def find(c) -> tuple[int, int]:
    for i in range(H):
        for j in range(W):
            if G[i][j] == c:
                return i, j

    assert False


def move_knight(r: int, c: int) -> list[tuple[int, int]]:
    #res = []
    for dr, dc in [(-2, 1), (-1, 2), (1, 2), (2, 1), (2, -1), (1, -2), (-1, -2), (-2, -1)]:
        nr = r + dr
        nc = c + dc
        if not (0 <= nr < H and 0 <= nc < W): continue
        #res.append((nr, nc))
        yield nr, nc

    #return res


def move_bishop(r: int, c: int) -> list[tuple[int, int]]:
    #res = []
    for dr, dc in [(-1, 1), (1, 1), (1, -1), (-1, -1)]:
        nr = r + dr
        nc = c + dc
        if not (0 <= nr < H and 0 <= nc < W): continue
        #res.append((nr, nc))
        yield nr, nc

    #return res


KNIGHT = 0
BISHOP = 1
start = find('S')

q = deque([(start[0], start[1], 0, 0)])
used = list3(H, W, 2, val=False)
while q:
    r, c, step, piece = q.popleft()
    if used[r][c][piece]: continue
    used[r][c][piece] = True

    if G[r][c] == 'G':
        print(step)
        break

    movefn = move_knight if piece == 0 else move_bishop
    for nr, nc in movefn(r, c):
        np = piece
        if G[nr][nc] == 'R':
            np ^= 1

        if used[nr][nc][np]: continue
        q.append((nr, nc, step+1, np))
else:
    print(-1)