import sys
from collections import deque

readline = sys.stdin.readline
input_value = readline().split()
H = int(input_value[0])
W = int(input_value[1])

grid = [None] * H
for h in range(H):
    grid[h] = readline().rstrip().replace('S', '.').replace('G', '.')

can_reach_goal = [[False] * W for _ in range(H)]

if grid[H-1][W-1] == '.':
    can_reach_goal[H-1][W-1] = True
    for y in range(H-1, -1, -1):
        for x in range(W-1, -1, -1):
            if grid[y][x] == '.':
                if y + 1 < H and can_reach_goal[y+1][x]:
                    can_reach_goal[y][x] = True
                if x + 1 < W and can_reach_goal[y][x+1]:
                    can_reach_goal[y][x] = True

row_has_reach = [[False] * W for _ in range(H)]
col_has_reach = [[False] * W for _ in range(H)]

for y in range(H):
    has_reach = False
    for x in range(W-1, -1, -1):
        if can_reach_goal[y][x]:
            has_reach = True
        row_has_reach[y][x] = has_reach

for x in range(W):
    has_reach = False
    for y in range(H-1, -1, -1):
        if can_reach_goal[y][x]:
            has_reach = True
        col_has_reach[y][x] = has_reach

dist = [[-1] * W for _ in range(H)]
queue = deque()
dist[0][0] = 0
queue.append((0,0))

dy = [-1, 1, 0, 0]
dx = [0, 0, -1, 1]
Magic = H + W
ans = -1
check_point = False

while queue:
    y, x = queue.popleft()
    if y == H - 1 and x == W - 1:
        ans = dist[y][x]
        break
    
    if dist[y][x] == y + x:
        if y + 1 < H and row_has_reach[y + 1][x]:
            check_point = True
        if x + 1 < W and col_has_reach[y][x + 1]:
            check_point = True
    
    for i in range(4):
        ny = y + dy[i]
        nx = x + dx[i]

        if 0 <= ny < H and 0 <= nx < W:
            if grid[ny][nx] == '.' and dist[ny][nx] == -1:
                dist[ny][nx] = dist[y][x] + 1
                queue.append((ny, nx))

if check_point:
    if ans == -1 or ans > Magic - 1:
        ans = Magic - 1
else:
    if ans == -1 or ans > Magic:
        ans = Magic

print(ans)