/*
* Problem link
* 
*/

#include<bits/stdc++.h>
using namespace std;

bool inner(int v, int lb, int ub) { return lb <= v&&v <=ub; }
struct INIT{INIT(){cin.tie(0);ios_base::sync_with_stdio(false);} }init;
const int INF = (int)1e7;
const int dr[2][8] = { {1,1,-1,-1,2,-2,2,-2},{ 1,1,-1,-1,1,1,-1,-1 } };
const int dc[2][8] = { {2,-2,2,-2,1,1,-1,-1},{ 1,-1,-1,1,1,-1,-1,1 } };
int main() {
#ifdef INPUT_FROM_FILE
	ifstream cin("sample.in");
	ofstream cout("sample.out");
#endif
	int R, C;
	cin >> R >> C;
	vector<string> S(R);
	for (auto& it : S)cin >> it;
	int sr, sc, gr, gc;
	for (int r = 0; r < R; r++)
		for (int c = 0; c < C; c++)
			if (S[r][c] == 'S')sr = r, sc = c;
		else if (S[r][c] == 'G')gr = r, gc = c;

	vector<vector<vector<int>>> NB(2,vector<vector<int>>(R, vector<int>(C, INF)));
	NB[0][sr][sc] = 0;
	queue<vector<int>> que;
	que.push(vector<int>{0, sr, sc});



	while (que.empty() == false) {
		auto v = que.front(); que.pop();
		int type = v[0];
		int r = v[1];
		int c = v[2];
		for (int i = 0; i < 8; i++) {
			int nr = r + dr[type][i];
			int nc = c + dc[type][i];
			if (inner(nr, 0, R - 1) && inner(nc, 0, C - 1)) {
				int nt = type ^ (S[nr][nc] == 'R');
				if (NB[nt][nr][nc]> NB[type][r][c] + 1) {
					NB[nt][nr][nc] = NB[type][r][c] + 1;
					que.push(vector<int>{nt, nr, nc});
				}
			}
		}
	}
	int res = min(NB[0][gr][gc], NB[1][gr][gc]);
	if (res == INF)res = -1;
	cout << res << endl;
	return 0;
}