#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; };

ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

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}};

int H, W;

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

int main() {
	cin >> H >> W;
	vector<string> a(H);
	int sy, sx, ty, tx;
	for (int y = 0; y < H; y++) {
		cin >> a[y];
		for (int x = 0; x < W; x++) {
			if (a[y][x] == 'S') sy = y, sx = x, a[y][x] = '.';
			if (a[y][x] == 'G') ty = y, tx = x, a[y][x] = '.';
		}
	}
	vector<vector<vector<int> > > d(H, vector<vector<int> >(W, vector<int>(2, INT_MAX)));
	d[sy][sx][0] = 0;
	queue<int> q;
	q.push(f(sy, sx, 0));
	while (!q.empty()) {
		int z = q.front(); q.pop();
		int y = z / 2 / W, x = z / 2 % W, t = z % 2;
		for (int k = 0; k < 8; k++) {
			int _y = y + dy[t][k], _x = x + dx[t][k];
			if (_y >= 0 && _y < H && _x >= 0 && _x < W) {
				int _t = t;
				if (a[_y][_x] == 'R') _t ^= 1;
				if (d[_y][_x][_t] > d[y][x][t] + 1) {
					d[_y][_x][_t] = d[y][x][t] + 1;
					q.push(f(_y, _x, _t));
				}
			}
		}
	}
	int ans = min(d[ty][tx][0], d[ty][tx][1]);
	if (ans == INT_MAX) ans = -1;
	cout << ans << endl;
}