import sys
input = sys.stdin.readline
from collections import deque

def bfs(sx, sy):
    dist = [[[-1] * W for _ in range(H)] for _ in range(2)]
    dist[0][sx][sy] = 0
    q = deque([])
    q.append((sx, sy, 0))
    
    while q:
        cx, cy, f = q.popleft()
        
        if f == 0:
            for nx, ny in [(cx+1, cy+2), (cx+1, cy-2), (cx+2, cy+1), (cx+2, cy-1), (cx-1, cy+2), (cx-1, cy-2), (cx-2, cy+1), (cx-2, cy-1)]:
                if 0<=nx<H and 0<=ny<W and S[nx][ny] == 'R':
                    if dist[1][nx][ny] == -1:
                        dist[1][nx][ny] = dist[0][cx][cy]+1
                        q.append((nx, ny, 1))
                elif 0<=nx<H and 0<=ny<W and S[nx][ny] != 'R':
                    if dist[0][nx][ny] == -1:
                        dist[0][nx][ny] = dist[0][cx][cy]+1
                        q.append((nx, ny, 0))
        elif f == 1:
            for nx, ny in [(cx+1, cy+1), (cx+1, cy-1), (cx-1, cy+1), (cx-1, cy-1)]:
                if 0<=nx<H and 0<=ny<W and S[nx][ny] == 'R':
                    if dist[0][nx][ny] == -1:
                        dist[0][nx][ny] = dist[1][cx][cy]+1
                        q.append((nx, ny, 0))
                elif 0<=nx<H and 0<=ny<W and S[nx][ny] != 'R':
                    if dist[1][nx][ny] == -1:
                        dist[1][nx][ny] = dist[1][cx][cy]+1
                        q.append((nx, ny, 1))
    
    return dist

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

for i in range(H):
    for j in range(W):
        if S[i][j] == 'S':
            sx, sy = i, j
        
        if S[i][j] == 'G':
            gx, gy = i, j
            
dist = bfs(sx, sy)

if dist[0][gx][gy] == -1 and dist[1][gx][gy] == -1:
    print(-1)
elif dist[0][gx][gy] == -1:
    print(dist[1][gx][gy])
elif dist[1][gx][gy] == -1:
    print(dist[0][gx][gy])
else:
    print(min(dist[0][gx][gy], dist[1][gx][gy]))