#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<b;i++)

typedef tuple<int, int, int> tiii;
typedef pair<tiii, int> pti;

int dx[2][8] = { { -2, -1, 1, 2, -2, -1, 1, 2 } ,{ -1, 1, -1, 1, 0, 0, 0, 0 } };
int dy[2][8] = { { -1, -2, -2, -1, 1, 2, 2, 1 } ,{ -1, -1, 1,1, 0, 0, 0, 0 } };
int dnum[2] = { 8, 4 };

int main()
{
	int H, W; cin >> H >> W;
	vector<string> s(H); rep(i, 0, H) cin >> s[i];

	int sx, sy;
	rep(y, 0, H) rep(x, 0, W) if (s[y][x] == 'S')
	{
		sx = x;
		sy = y;
	}

	set<tiii> done;
	queue<pti> que;

	que.push(pti(tiii(sx, sy, 0), 0));
	while (!que.empty())
	{
		pti p = que.front(); que.pop();

		if (done.find(p.first) != done.end()) continue;
		done.insert(p.first);

		int x = get<0>(p.first);
		int y = get<1>(p.first);
		int type = get<2>(p.first);
		int cost = p.second;

		//printf("(%d,%d,%d,%d)\n", x, y, type, cost);

		if (s[y][x] == 'G')
		{
			cout << cost << endl;
			return 0;
		}

		rep(i, 0, dnum[type])
		{
			int xx = x + dx[type][i];
			int yy = y + dy[type][i];
			
			if (xx < 0 || W <= xx) continue;
			if (yy < 0 || H <= yy) continue;

			int ttype;
			if (s[yy][xx] == 'R')
				ttype = (type + 1) % 2;
			else
				ttype = type;

			que.push(pti(tiii(xx, yy, ttype),cost + 1));
		}
	}
	cout << -1 << endl;
}