#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll, ll> P;

#define EACH(i,a) for (auto& i : a)
#define FOR(i,a,b) for (ll i=(a);i<(b);i++)
#define RFOR(i,a,b) for (ll i=(b)-1;i>=(a);i--)
#define REP(i,n) for (ll i=0;i<(n);i++)
#define RREP(i,n) for (ll i=(n)-1;i>=0;i--)
#define debug(x) cout<<#x<<": "<<x<<endl
#define pb push_back
#define ALL(a) (a).begin(),(a).end()

const ll linf = 1e18;
const int inf = 1e9;
const double eps = 1e-12;
const double pi = acos(-1);

template<typename T>
istream& operator>>(istream& is, vector<T>& vec) {
	EACH(x,vec) is >> x;
	return is;
}
/*
template<class... T>
ostream& operator<<(ostream& os, tuple<T...>& t) {
	for (size_t i = 0; i < tuple_size< tuple<T...> >::value; ++i) {
		if (i) os << " ";
		os << get<0>(t);
	}
	return os;
}
*/
template<typename T>
ostream& operator<<(ostream& os, vector<T>& vec) {
	REP(i,vec.size()) {
		if (i) os << " ";
		os << vec[i];
	}
	return os;
}
template<typename T>
ostream& operator<<(ostream& os, vector< vector<T> >& vec) {
	REP(i,vec.size()) {
		if (i) os << endl;
		os << vec[i];
	}
	return os;
}

struct Node {
	int x, y, mode, cost;
};
bool operator>(const Node& n1, const Node& n2) {
	return n1.cost > n2.cost;
}

int H, W;
vector<string> m;
bool inRange(int x, int y) {
	return 0 <= x && x < W && 0 <= y && y < H;
}
vector< vector<P> > nxt = {
	{{1, 2}, {2, 1}, {1, -2}, {2, -1}, {-1, 2}, {-2, 1}, {-1, -2}, {-2, -1}},
	{{1, 1}, {1, -1}, {-1, 1}, {-1, -1}},
};
int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(0);
	cin >> H >> W;
	m.resize(H); cin >> m;
	int sx, sy, gx, gy;
	REP(y, H) REP(x, W) {
		if (m[y][x] == 'S') {
			m[y][x] = '.';
			sx = x, sy = y;
		}
		else if (m[y][x] == 'G') {
			m[y][x] = '.';
			gx = x, gy = y;
		}
	}
	vector< vector< vector<int> > > dist(H, vector< vector<int> >(W, vector<int>(2, inf)));
	priority_queue<Node, vector<Node>, greater<Node> > Q; Q.push({sx, sy, 0, 0});
	while ( !Q.empty() ) {
		Node node = Q.top(); Q.pop();
		int x = node.x, y = node.y, cost = node.cost, mode = node.mode;
		// cout << x << " " << y << " " << mode << " " << cost << endl;
		if (cost > dist[y][x][mode]) continue;
		REP(i, nxt[mode].size()) {
			int nx = x + nxt[mode][i].first;
			int ny = y + nxt[mode][i].second;
			if ( !inRange(nx, ny) ) continue;
			int nm = m[ny][nx] == 'R' ? !mode : mode;
			if ( cost+1 < dist[ny][nx][nm] ) {
				dist[ny][nx][nm] = cost+1;
				Q.push({nx, ny, nm, dist[ny][nx][nm]});
			}
		}
	}
	int ans = inf;
	REP(i, 2) ans = min(ans, dist[gy][gx][i]);
	if (ans == inf) cout << -1 << endl;
	else cout << ans << endl;
}