#include<iostream>
#include<queue>
#include<tuple>
#include<vector>
using namespace std;

#define INF 100000000
#define ISREAD 'R'
#define ISWHITE '.'
#define ISKNIGHT	true
#define ISBISHOP	false

int knightdx[8] = { 1, 2, 2, 1, -1, -2, -2, -1 };
int knightdy[8] = { -2, -1, 1, 2, 2, 1, -1, -2 };
int bishopdx[4] = { 1, 1, -1, -1 };
int bishopdy[4] = { -1, 1, 1, -1 };

int main()
{
	int h, w, i, j;
	pair<int, int> start, goal;
	queue < tuple<int, int, bool>> que;
	cin >> h >> w;
	vector<vector<int>>	d(h, vector<int>(w, 0));
	vector<vector<char>> map(h, vector<char>(w));
	for (i = 0; i < h; ++i)
		for (j = 0; j < w; ++j) {
			cin >> map[i][j];
			if (map[i][j] == 'S') {
				map[i][j] = '.';
				start = pair<int, int>(i, j);
			}
			if (map[i][j] == 'G') {
				map[i][j] = '.';
				goal = pair<int, int>(i, j);
			}
		}
	que.push(tuple<int, int, bool>(start.first, start.second, ISKNIGHT));
	while (que.size()) {
		tuple<int, int, bool> t = que.front(); que.pop();
		int x0 = get<0>(t);
		int y0 = get<1>(t);
		bool state0 = get<2>(t);
		bool state = state0;
		switch (state0) {
		case ISKNIGHT:
			for (i = 0; i < 8; ++i) {
				int x = x0 + knightdx[i];
				int y = y0 + knightdy[i];
				if (0 <= x && x < h && 0 <= y && y < w && d[x][y] == 0)
				{
					d[x][y] = d[x0][y0] + 1;
					if (map[x][y] == 'R')state = !state0;
					que.push(tuple<int, int, bool>{x, y, state});
					state = state0;
				}
			}
			break;
		case ISBISHOP:
			for (i = 0; i < 4; ++i) {
				int x = x0 + bishopdx[i];
				int y = y0 + bishopdy[i];
				if (0 <= x && x < h && 0 <= y && y < w && d[x][y] == 0)
				{
					d[x][y] = d[x0][y0] + 1;
					if (map[x][y] == 'R')state = !state0;
					que.push(tuple<int, int, bool>{x, y, state});
					state = state0;
				}
			}
			break;
		}
	}
	if (d[goal.first][goal.second])cout << d[goal.first][goal.second] << endl;
	else cout << -1 << endl;
	return 0;
}