#include <bits/stdc++.h>

using namespace std;

#define endl '\n'
#define PB push_back
#define ALL(a)  (a).begin(),(a).end()
#define SZ(a) int((a).size())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n)  FOR(i,0,n)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define RBP(i,a) for(auto& i : a)
#ifdef LOCAL111
	#define DEBUG(x) cout<<#x<<": "<<(x)<<endl
#else
	#define DEBUG(x)
#endif
#define F first
#define S second
#define SNP string::npos
#define WRC(hoge) cout << "Case #" << (hoge)+1 << ": "
#define INF 1e8

typedef pair<int,int> P;
typedef long long int LL;
typedef unsigned long long ULL;
typedef pair<LL,LL> LP;

void ios_init(){ ios::sync_with_stdio(false); cin.tie(0);	
	//cout.setf(ios::fixed);
	//cout.precision(12);
}

int dx[] = {0,1,0,-1};
int dy[] = {0,-1,0,1};
int ddx[] = {1,-1,1,-1};
int ddy[] = {-1,1,1,-1};

int main()
{
	ios_init();
	int h,w;
	cin >> h >> w;
	vector<string> s(h);
	REP(i,h){
		cin >> s[i];
	}
	int sx, sy, gx, gy;
	REP(i,h){
		REP(j,w){
			if(s[i][j] == 'S'){
				sx = i;
				sy = j;
			}else if(s[i][j] == 'G'){
				gx = i;
				gy = j;
			}
		}
	}
	vector<tuple<bool,int,int>> g[2][h][w];
	REP(i,h){
		REP(j,w){
			REP(k,4){
				int dx = ddx[k], dy = ddy[k];
			//	cout << endl;
				DEBUG(i); DEBUG(j);
				int ni = i+dx, nj = j+dy*2;
				DEBUG(ni); DEBUG(nj);
				if(0 <= ni and ni < h and 0 <= nj and nj < w){
					if(s[ni][nj] != 'R'){
						g[0][i][j].push_back(make_tuple(0,ni,nj));
					}else{
						g[0][i][j].push_back(make_tuple(1,ni,nj));
					}
				}
				ni = i+2*dx;
				nj = j+dy;
				DEBUG(ni); DEBUG(nj);
				if(0 <= ni and ni < h and 0 <= nj and nj < w){
					if(s[ni][nj] != 'R'){
						g[0][i][j].push_back(make_tuple(0,ni,nj));
					}else{
						g[0][i][j].push_back(make_tuple(1,ni,nj));
					}
				}
			}
		}
	}
	REP(i,h){
		REP(j,w){
			REP(k,4){
				int ni = i+dx[k], nj = j+dy[k];
				if(0 <= ni and ni < h and 0 <= nj and nj < w){
					if(s[ni][nj] != 'R'){
						g[1][i][j].push_back(make_tuple(1,ni,nj));
					}else{
						g[1][i][j].push_back(make_tuple(0,ni,nj));
					}
				}
			}
		}
	}
	bool gf[2][h][w];
	fill(gf[0][0],gf[2][0],false);
	queue<tuple<bool,int,int,int>> qu;
	qu.push(make_tuple(0,sx,sy,0));
	while(!qu.empty()){
		auto t = qu.front();
		qu.pop();
		int a = get<0>(t);
		int b = get<1>(t);
		int c = get<2>(t);
		if(b == gx and c == gy){
			cout << get<3>(t) << endl;
			return 0;
		}
		gf[a][b][c] = true;
		RBP(tup,g[a][b][c]){
			if(!gf[get<0>(tup)][get<1>(tup)][get<2>(tup)]){
				qu.push(tuple_cat(tup,make_tuple(get<3>(t)+1)));
			}
		}
	}
	cout << -1 << endl;
	return 0;
}