import pypyjit
pypyjit.set_param('max_unroll_recursion=-1')
H,W = map(int,input().split())
S = [list(input()) for _ in range(H)]
for i in range(H):
    for j in range(W):
        if S[i][j] == 'S':
            s = (i,j)
        if S[i][j] == 'G':
            g = (i,j)
            

from collections import deque
v = deque()

dist = [[[-1]*W for _ in range(H)] for j in range(2)]

v.append((0,s[0],s[1]))
dist[0][s[0]][s[1]]=0


def nb1(i,j):
    dx = [1,1,2,2,-1,-1,-2,-2]
    dy = [2,-2,1,-1,2,-2,1,-1]
    tmp = []
    for t in range(8):
        tx = dx[t]+i
        ty = dy[t]+j
        if (0<=tx<H)&(0<=ty<W):
            tmp.append((tx,ty))
    return tmp
 
 
def nb2(i,j):
    dx = [1,1,-1,-1]
    dy = [1,-1,1,-1]
    tmp = []
    for t in range(4):
        tx = dx[t]+i
        ty = dy[t]+j
        if (0<=tx<H)&(0<=ty<W):
            tmp.append((tx,ty))
    return tmp   


while v:
    
    ic,ix,iy = v.popleft()
    td = dist[ic][ix][iy]
    
    if ic==0:
        for jx,jy in nb1(ix,iy):
            
            if S[jx][jy]=='R':
                
                if dist[1][jx][jy]==-1:
                    dist[1][jx][jy] = td+1
                    v.append((1,jx,jy))
            else:
                if dist[0][jx][jy]==-1:
                    dist[0][jx][jy] = td+1
                    v.append((0,jx,jy))        
    else:
        
        for jx,jy in nb2(ix,iy):
            
            if S[jx][jy]=='R':
                
                if dist[0][jx][jy]==-1:
                    dist[0][jx][jy] = td+1
                    v.append((0,jx,jy))
            else:
                if dist[1][jx][jy]==-1:
                    dist[1][jx][jy] = td+1
                    v.append((1,jx,jy))            
                
a = dist[0][g[0]][g[1]]
b = dist[1][g[0]][g[1]]

if (a==-1)&(b==-1):
    print(-1)
elif (a!=-1)&(b!=-1):
    print(min(a,b))
else:
    print(max(a,b))