def nin():
    return list(map(int,input().split()))

import collections
import random
h,w=nin()
s=[list(input()) for i in range(h)]
#h=w=2*10**3
#s=[["#" for _ in range(h)] for _ in range(h)]
#s[0][0]="S"
#azs[-1][-1]="G"
hh=2*h-1
ww=2*w-1
ss=gg=-1
black=set()
dij=[1,-1,ww+2,-(ww+2)]
dij2=[2*i for i in dij]
di2=[2*(ww+2),2*(-(ww+2))]
dj2=[2,-2]
d=[-1]*((hh+2)*(ww+2))
for i in range(h):
    for j in range(w):
        if s[i][j]=="S":
            ss=2*i*(ww+2)+2*j
            s[i][j]="."
        elif s[i][j]=="G":
            gg=2*i*(ww+2)+2*j
            s[i][j]="."
        elif s[i][j]=="#":
            d[2*i*(ww+2)+2*j]=-2
for i in [hh,hh+1]:
    for j in range(ww+2):
        d[i*(ww+2)+j]=-2
for i in range(hh+2):
    for j in [ww,ww+1]:
        d[i*(ww+2)+j]=-2
task=collections.deque()
task.append(ss)
d[ss]=0
ww2=ww+2
while len(task)>0:
    i=task.popleft()
    ii,jj=i//ww2,i%ww2
    rin=[]
    for D in dij:
        if d[i+D]!=-2:
            rin.append(i+D)
    if ii%2==jj%2==0:
        for D in dij2:
            if d[i+D]!=-2:
                rin.append(i+D)
    if ii%2==0 and jj%2==1:
        for D in di2:
            if d[i+D]!=-2:
                rin.append(i+D)
    if ii%2==1 and jj%2==0:
        for D in dj2:
            if d[i+D]!=-2:
                rin.append(i+D)
    
    for j in rin:
        if d[j]==-1:
            d[j]=d[i]+1
            if j==gg:
                print(d[j])
                exit()
            task.append(j)