#include <algorithm>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <ostream>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
#define INF 1000000000
#define rep(i,a,b) for (int i=(a);i<(b);i++)
#define rev(i,a,b) for (int i=(a)-1;i>=b;i--)
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef queue<int> qi;
typedef vector<int> vi;
typedef vector<string> vs;
int dx[4] = { 0, 1, 0, -1 };
int dy[4] = { 1, 0, -1, 0 };

int h, w;
char s[500][501];
int m[2][500][500];

int nmx[] = { 1,  2,  -1, -2, 1, 2, -1, -2};
int nmy[] = {-2, -1,  -2, -1, 2, 1,  2,  1};
int bmx[] = {1,  1, -1, -1};
int bmy[] = {1, -1,  1, -1};

void solve() {
	int sx, sy;
	rep(i,0,h)
	 rep(j,0,w) {
			if(s[i][j] == 'S') {
				sy = i;
				sx = j;
			}
		}

	rep(i,0,h)
		rep(j,0,w) {
		m[0][i][j] = INF;
		m[1][i][j] = INF;
		}

	qi qx, qy, qt, qbt;
	qx.push(sx);
	qy.push(sy);
	qt.push(0);
	qbt.push(0);
	m[0][sy][sx] = 0;

	while(!qx.empty()) {
		int x = qx.front();
		int y = qy.front();
		int t = qt.front();
		int bt = qbt.front();
		qx.pop();
		qy.pop();
		qt.pop();
		qbt.pop();

		if(s[y][x] == 'G') {
			cout << min(m[0][y][x], m[1][y][x]) << endl;
			return ;
		}

		if(t == 0) {
			rep(i,0,8) {
				int mx = x + nmx[i];
				int my = y + nmy[i];
				if(0 <= mx && mx < w && 0 <= my && my < h) {
					if(s[my][mx] == 'R') {
						if(m[1][my][mx] != INF) continue;
						qt.push(1);
						m[1][my][mx] = m[t][y][x] + 1;
					} else {
						if(m[0][my][mx] != INF) continue;
						qt.push(0);
						m[0][my][mx] = m[t][y][x] + 1;
					}
					qbt.push(t);
					qx.push(mx);
					qy.push(my);
				}
			}
		} else {
			rep(i,0,4) {
				int mx = x + bmx[i];
				int my = y + bmy[i];
				if(0 <= mx && mx < w && 0 <= my && my < h) {
					if(s[my][mx] == 'R') {
						if(m[0][my][mx] != INF) continue;
						qt.push(0);
						m[0][my][mx] = m[t][y][x] + 1;
					} else {
						if(m[1][my][mx] != INF) continue;
						qt.push(1);
						m[1][my][mx] = m[t][y][x] + 1;
					}
					qbt.push(t);
					qx.push(mx);
					qy.push(my);
				}
			}
		}
	}
	cout << "-1" << endl;
}

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	cin >> h >> w;
	rep(i,0,h) cin >> s[i];
	solve();

	return 0;
}