from collections import deque
import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def SI(): return sys.stdin.readline()[:-1]
dij0=[(1,2),(2,1),(-1,-2),(-2,-1),(1,-2),(-2,1),(-1,2),(2,-1)]
dij1=[(1,1),(-1,1),(1,-1),(-1,-1)]

def main():
    h,w=MI()
    ss=[[0]*w for _ in range(h)]
    for i in range(h):
        for j,c in enumerate(SI()):
            if c=="R":ss[i][j]=1
            if c=="S":si,sj=i,j
            if c=="G":gi,gj=i,j
    fin=[[[False]*2 for _ in range(w)] for _ in range(h)]
    q=deque()
    q.append((0,si,sj,0))
    fin[si][sj][0]=0
    while q:
        d,i,j,k=q.popleft()
        if ss[i][j]:k=1-k
        dij=dij1 if k else dij0
        for di,dj in dij:
            ni,nj=i+di,j+dj
            if (ni,nj)==(gi,gj):
                print(d+1)
                exit()
            if ni<0 or nj<0 or ni>=h or nj>=w:continue
            if fin[ni][nj][k]:continue
            fin[ni][nj][k]=True
            q.append((d+1,ni,nj,k))
    print(-1)

main()