#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };

int INF = INT_MAX / 2;
ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

vector<int> bfs(int N, vector<vector<int> >& G, int s) {
	vector<int> d(N, INF); d[s] = 0;
	queue<int> q; q.push(s);
	while (q.size()) {
		int u = q.front(); q.pop();
		for (int v: G[u])
			if (d[v] > d[u] + 1) {
				d[v] = d[u] + 1;
				q.push(v);
			}
	}
	return d;
}

int H, W;

int f(int y, int x, int z) {
	return (y * W + x) * 2 + z;
}

int main() {
	cin >> H >> W;
	vector<string> a(H);
	int ys, xs, yt, xt;
	for (int y = 0; y < H; y++) {
		cin >> a[y];
		for (int x = 0; x < W; x++) {
			char& c = a[y][x];
			if (c == 'S') ys = y, xs = x, c = '.';
			if (c == 'G') yt = y, xt = x, c = '.';
		}
	}
	int N = H * W * 2;
	vector<vector<int> > G(N);
	for (int y = 0; y < H; y++)
		for (int x = 0; x < W; x++)
			for (int z = 0; z <= 1; z++) {
				int dy[2][8] = {{-1, -2, -2, -1, 1, 2, 2, 1}, {-1, -1, 1, 1, -1, -1, 1, 1}};
				int dx[2][8] = {{-2, -1, 1, 2, 2, 1, -1, -2}, {-1, 1, 1, -1, -1, 1, 1, -1}};
				for (int k = 0; k < 8; k++) {
					int _y = y + dy[z][k], _x = x + dx[z][k];
					if (_y >= 0 && _y < H && _x >= 0 && _x < W) {
						int _z = z;
						if (a[_y][_x] == 'R') _z ^= 1;
						G[f(y, x, z)].push_back(f(_y, _x, _z));
					}
				}
			}
	vector<int> d = bfs(N, G, f(ys, xs, 0));
	int ans = min(d[f(yt, xt, 0)], d[f(yt, xt, 1)]);
	if (ans == INF) ans = -1;
	cout << ans << endl;
}