#include<bits/stdc++.h>
#define ll long long
#define endl '\n'
#define pr(x) pair<x,x>
#define up(i,j,k,l) for(int i=j;i<=k;i+=l)
#define down(i,j,k,l) for(int i=j;i>=k;i-=l)
using namespace std;
const int N=1e3+10;
const int dx[4]={0,1,-1,0},dy[4]={1,0,0,-1};
int h,w;
char a[N][N];
bool f[N][N];
struct node{
	int x,y,t,d;
};
queue< node > q;
int sx,sy,ex,ey;
bool check(int x,int y)
{
	if(x<1 || y<1 || x>h || y>w || a[x][y]=='#' || f[x][y]==true){
		return false;
	}
	else{
		return true;
	}
}
void bfs()
{
	q.push({sx,sy,-1,0});
	f[sx][sy]=true;
	int tx,ty,xx,yy,tt,dd;
	while(!q.empty()){
		xx=q.front().x;
		yy=q.front().y;
		tt=q.front().t;
		dd=q.front().d;
		q.pop();
		if(xx==ex && yy==ey){
			cout<<dd<<endl;
			return;
		}
		up(i,0,3,1){
			tx=dx[i]+xx;
			ty=dy[i]+yy;
			if(check(tx,ty)){
				if(tt==1 && (i==0 || i==3)){
					continue;
				}
				if(tt==2 && (i==1 || i==2)){
					continue;
				}
				f[tx][ty]=true;
				if((i==0 || i==3)){
					q.push({tx,ty,1,dd+1});
				}
				if((i==1 || i==2)){
					q.push({tx,ty,2,dd+1});
				}
			}
		}
	}
	cout<<-1<<endl;
	return;
}
void solve()
{
	cin>>h>>w;
	up(i,1,h,1){
		up(j,1,w,1){
			cin>>a[i][j];
			if(a[i][j]=='S'){
				sx=i;
				sy=j;
			}
			if(a[i][j]=='G'){
				ex=i;
				ey=j;
			}			
		}
	}
	bfs();
	return;
}
int main()
{
    //ios::sync_with_stdio(false);
	//cin.tie(0);
	//freopen(".in","r",stdin);
	//freopen(".out","w",stdout);
	int _=1;
	//cin>>_;
	up(i,1,_,1){
		solve();
	}
	return 0;
}