using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Collections.Generic;
using System.Diagnostics;
using System.Numerics;
using Enu = System.Linq.Enumerable;

public class Program
{
    static readonly int INF = (int)1e9;
    static readonly int[][] DR = { new[] { -2, -2, 2, 2, -1, -1, 1, 1 }, new[] { -1, -1, 1, 1 } };
    static readonly int[][] DC = { new[] { -1, 1, -1, 1, -2, 2, -2, 2 }, new[] { -1, 1, -1, 1 } };


    public void Solve()
    {
        int H = Reader.Int(), W = Reader.Int();
        var grid = Reader.StringArray(H);
        int sr = 0, sc = 0, gr = 0, gc = 0;
        for (int r = 0; r < H; r++)
            for (int c = 0; c < W; c++)
                if (grid[r][c] == 'S') { sr = r; sc = c; }
                else if (grid[r][c] == 'G') { gr = r; gc = c; }
        var minSteps = new int[H, W, 2];
        Fill(minSteps, INF);
        minSteps[sr, sc, 0] = 0;
        var que = new Queue<int>();
        que.Enqueue(sr); que.Enqueue(sc); que.Enqueue(0);
        Func<int, int, bool> IsInside = (r, c) => r >= 0 && r < H && c >= 0 && c < W;

        while (que.Count > 0)
        {
            int r = que.Dequeue(), c = que.Dequeue(), type = que.Dequeue();
            for (int d = 0; d < DR[type].Length; d++)
            {
                int nr = r + DR[type][d], nc = c + DC[type][d];
                if (IsInside(nr, nc))
                {
                    int nextType = type ^ (grid[nr][nc] == 'R' ? 1 : 0);
                    if (minSteps[nr, nc, nextType] == INF)
                    {
                        if (nr == gr && nc == gc) { Console.WriteLine(minSteps[r, c, type] + 1); return; }
                        minSteps[nr, nc, nextType] = minSteps[r, c, type] + 1;
                        que.Enqueue(nr); que.Enqueue(nc); que.Enqueue(nextType);
                    }
                }
            }

        }

        Console.WriteLine(-1);
    }

    void Fill<T>(T[, ,] a, T val)
    {
        for (int i = 0; i < a.GetLength(0); i++)
            for (int j = 0; j < a.GetLength(1); j++)
                for (int k = 0; k < a.GetLength(2); k++)
                    a[i, j, k] = val;
    }
}


class Entry { static void Main() { new Program().Solve(); } }
class Reader
{
    static TextReader reader = Console.In;
    static readonly char[] separator = { ' ' };
    static readonly StringSplitOptions op = StringSplitOptions.RemoveEmptyEntries;
    static string[] A = new string[0];
    static int i;
    static void Init() { A = new string[0]; }
    public static void Set(TextReader r) { reader = r; Init(); }
    public static void Set(string file) { reader = new StreamReader(file); Init(); }
    public static bool HasNext() { return CheckNext(); }
    public static string String() { return Next(); }
    public static int Int() { return int.Parse(Next()); }
    public static long Long() { return long.Parse(Next()); }
    public static double Double() { return double.Parse(Next()); }
    public static int[] IntLine() { return Array.ConvertAll(Split(Line()), int.Parse); }
    public static int[] IntArray(int N) { return Range(N, Int); }
    public static int[][] IntTable(int H) { return Range(H, IntLine); }
    public static string[] StringArray(int N) { return Range(N, Next); }
    public static string[][] StringTable(int N) { return Range(N, () => Split(Line())); }
    public static string Line() { return reader.ReadLine().Trim(); }
    static T[] Range<T>(int N, Func<T> f) { return Enu.Range(0, N).Select(i => f()).ToArray(); }
    static string[] Split(string s) { return s.Split(separator, op); }
    static string Next() { CheckNext(); return A[i++]; }
    static bool CheckNext()
    {
        if (i < A.Length) return true;
        string line = reader.ReadLine();
        if (line == null) return false;
        if (line == "") return CheckNext();
        A = Split(line);
        i = 0;
        return true;
    }
}