#!/usr/bin/env python3

import array
import collections


DS_KNIGHT = [(1, 2), (-1, -2), (1, -2), (-1, 2), (2, 1), (-2, -1), (2, -1), (-2, 1)]
DS_MB = [(1, 1), (-1, -1), (1, -1), (-1, 1)]
INF = 10 ** 8
Status = collections.namedtuple("Status", "is_knight r c")


def min_num_of_operations(height, width, board, start, goal):
    s_start = Status(True, start[0], start[1])
    dist = [[array.array("L", (INF for _ in range(width))) for _ in range(height)] for _ in range(2)]
    dist[s_start.is_knight][s_start.r][s_start.c] = 0
    q = collections.deque()
    q.append(s_start)
    while q:
        s0 = q.popleft()
        if (s0.r, s0.c) == goal:
            break
        for dr, dc in (DS_KNIGHT if s0.is_knight else DS_MB):
            (r, c) = (s0.r + dr, s0.c + dc)
            if r < 0 or r >= height or c < 0 or c >= width:
                continue
            else:
                new_type = s0.is_knight ^ (board[r][c] == 'R')
                if dist[int(new_type)][r][c] >= INF:
                    s = Status(new_type, r, c)
                    q.append(s)
                    dist[int(new_type)][r][c] = dist[int(s0.is_knight)][s0.r][s0.c] + 1
    return min(dist[True][goal[0]][goal[1]], dist[False][goal[0]][goal[1]])


def main():
    height, width = map(int, input().split())
    board = []
    start = None
    goal = None
    for r in range(height):
        row = input()
        if start is None or goal is None:
            for c in range(width):
                if row[c] == "S":
                    start = (r, c)
                elif row[c] == "G":
                    goal = (r, c)
        board.append(row)
    ans = min_num_of_operations(height, width, board, start, goal)
    print(ans if ans < INF else -1)


if __name__ == '__main__':
    main()