using System;
using System.Collections.Generic;
using System.Linq;

//No367 ナイトの転身
class Program
{
    static string InputPattern = "InputX";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("4 4");
            WillReturn.Add("...G");
            WillReturn.Add(".RR.");
            WillReturn.Add(".RR.");
            WillReturn.Add("S...");
            //3
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("3 4");
            WillReturn.Add("...G");
            WillReturn.Add("....");
            WillReturn.Add("S...");
            //3
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("3 3");
            WillReturn.Add(".R.");
            WillReturn.Add("RGR");
            WillReturn.Add("SR.");
            //-1
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static int UB_X;
    static int UB_Y;

    struct JyoutaiDef
    {
        internal int Level;
        internal int CurrX;
        internal int CurrY;
        internal bool IsKnight;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();

        int[] wkArr = InputList[0].Split(' ').Select(X => int.Parse(X)).ToArray();
        int H = wkArr[0];
        int W = wkArr[1];
        char[,] BanArr = new char[W, H];
        UB_X = W - 1;
        UB_Y = H - 1;

        int StaX = -1, StaY = -1, GoalX = -1, GoalY = -1;
        for (int X = 0; X <= UB_X; X++) {
            for (int Y = 0; Y <= UB_Y; Y++) {
                BanArr[X, Y] = InputList[Y + 1][X];

                if (BanArr[X, Y] == 'S') {
                    StaX = X; StaY = Y;
                }
                if (BanArr[X, Y] == 'G') {
                    GoalX = X; GoalY = Y;
                }
            }
        }

        var Que = new Queue<JyoutaiDef>();
        JyoutaiDef WillEnqueue;
        WillEnqueue.Level = 0;
        WillEnqueue.CurrX = StaX;
        WillEnqueue.CurrY = StaY;
        WillEnqueue.IsKnight = true;
        Que.Enqueue(WillEnqueue);

        var VisitedSet = new HashSet<int>();
        VisitedSet.Add(GetHash(WillEnqueue));
        while (Que.Count > 0) {
            JyoutaiDef Dequeued = Que.Dequeue();

            //クリア判定
            if (Dequeued.CurrX == GoalX && Dequeued.CurrY == GoalY) {
                Console.WriteLine(Dequeued.Level);
                return;
            }

            Action<int, int> EnqueueSyori = (pNewX, pNewY) =>
            {
                if (pNewX < 0 || UB_X < pNewX) return;
                if (pNewY < 0 || UB_Y < pNewY) return;

                WillEnqueue.Level = Dequeued.Level + 1;
                WillEnqueue.CurrX = pNewX;
                WillEnqueue.CurrY = pNewY;
                WillEnqueue.IsKnight = Dequeued.IsKnight;
                if (BanArr[pNewX, pNewY] == 'R') {
                    WillEnqueue.IsKnight = !WillEnqueue.IsKnight;
                }

                //再訪は不可
                if (VisitedSet.Add(GetHash(WillEnqueue)) == false)
                    return;

                Que.Enqueue(WillEnqueue);
            };

            if (Dequeued.IsKnight) {
                EnqueueSyori(Dequeued.CurrX - 1, Dequeued.CurrY - 2);
                EnqueueSyori(Dequeued.CurrX + 1, Dequeued.CurrY - 2);
                EnqueueSyori(Dequeued.CurrX - 2, Dequeued.CurrY - 1);
                EnqueueSyori(Dequeued.CurrX + 2, Dequeued.CurrY - 1);
                EnqueueSyori(Dequeued.CurrX - 2, Dequeued.CurrY + 1);
                EnqueueSyori(Dequeued.CurrX + 2, Dequeued.CurrY + 1);
                EnqueueSyori(Dequeued.CurrX - 1, Dequeued.CurrY + 2);
                EnqueueSyori(Dequeued.CurrX + 1, Dequeued.CurrY + 2);
            }
            else {
                EnqueueSyori(Dequeued.CurrX - 1, Dequeued.CurrY - 1);
                EnqueueSyori(Dequeued.CurrX + 1, Dequeued.CurrY - 1);
                EnqueueSyori(Dequeued.CurrX - 1, Dequeued.CurrY + 1);
                EnqueueSyori(Dequeued.CurrX + 1, Dequeued.CurrY + 1);
            }
        }
        Console.WriteLine(-1);
    }

    //現在位置とIsKnightからハッシュ値を求める
    static int GetHash(JyoutaiDef pJyoutai)
    {
        int Hash = pJyoutai.CurrX * 10000;
        Hash += pJyoutai.CurrY * 10;
        Hash += (pJyoutai.IsKnight ? 1 : 0);
        return Hash;
    }
}