h,w = map(int,input().split())
b = [input() for _ in range(h)]
for i in range(h):
    for j in range(w):
        if b[i][j] == "S":
            si,sj = i,j
        elif b[i][j] == "G":
            gi,gj = i,j
from collections import deque
INF = 10**9
dist = [[[INF]*w for _ in range(h)] for _ in range(2)]
dist[0][si][sj] = 0
q = deque([(0,si,sj)])
while q:
    kind,i,j = q.popleft()
    d = dist[kind][i][j]
    if kind == 0:
        for ni,nj in [(i-1,j-2),(i-1,j+2),(i+1,j-2),(i+1,j+2),(i-2,j-1),(i-2,j+1),(i+2,j-1),(i+2,j+1)]:
            if 0 <= ni < h and 0 <= nj < w:
                nkind = kind^(b[ni][nj] == "R")
                if dist[nkind][ni][nj] == INF:
                    dist[nkind][ni][nj] = d+1
                    q.append((nkind,ni,nj))
    else:
        for ni,nj in [(i-1,j-1),(i+1,j-1),(i-1,j+1),(i+1,j+1)]:
            if 0 <= ni < h and 0 <= nj < w:
                nkind = kind^(b[ni][nj] == "R")
                if dist[nkind][ni][nj] == INF:
                    dist[nkind][ni][nj] = d+1
                    q.append((nkind,ni,nj))
ans = min(dist[0][gi][gj],dist[1][gi][gj])
print(ans if ans != INF else -1)