using System;
using System.Collections.Generic;

namespace No367_1{
    public class Program{
        public static void Main(string[] args){
            var move = new[]{
                new[]{
                    new{X = -2, Y = -1},
                    new{X = -2, Y = +1},
                    new{X = -1, Y = -2},
                    new{X = -1, Y = +2},
                    new{X = +1, Y = -2},
                    new{X = +1, Y = +2},
                    new{X = +2, Y = -1},
                    new{X = +2, Y = +1}
                },
                new[]{
                    new{X = -1, Y = -1},
                    new{X = -1, Y = +1},
                    new{X = +1, Y = -1},
                    new{X = +1, Y = +1}
                }
            };

            var input = Console.ReadLine().Split(' ');
            var w = int.Parse(input[1]);
            var h = int.Parse(input[0]);

            var start = new Point(0, 0);
            var goal = new Point(0, 0);
            var map = new char[h][];
            for(var i = 0; i < h; i++){
                map[i] = Console.ReadLine().ToCharArray();
                int x;
                if((x = Array.IndexOf(map[i], 'S')) != -1){
                    start = new Point(x, i);
                }
                if((x = Array.IndexOf(map[i], 'G')) != -1){
                    goal = new Point(x, i);
                }
            }

            var result = new int[w, h, 2];
            result[start.X, start.Y, 0] = 1;
            var que = new Queue<Stat>();
            que.Enqueue(new Stat(start.X, start.Y, 0));

            while(que.Count != 0){
                var now = que.Dequeue();
                foreach(var m in move[now.Type]){
                    if(0 <= now.X + m.X && now.X + m.X < w && 0 <= now.Y + m.Y && now.Y + m.Y < h){
                        var next = new Stat(
                            now.X + m.X,
                            now.Y + m.Y,
                            map[now.Y + m.Y][now.X + m.X] == 'R' ? 1 - now.Type : now.Type
                            );
                        if(result[next.X, next.Y, next.Type] == 0 || result[next.X, next.Y, next.Type] > result[now.X, now.Y, now.Type] + 1){
                            que.Enqueue(next);
                            result[next.X, next.Y, next.Type] = result[now.X, now.Y, now.Type] + 1;
                        }
                    }
                }
            }

            
            if((result[goal.X, goal.Y, 0] == result[goal.X, goal.Y, 1]) && result[goal.X, goal.Y, 0] == 0){
                Console.WriteLine(-1);
            } else{
                if(result[goal.X, goal.Y, 0] == 0) result[goal.X, goal.Y, 0] = int.MaxValue;
                if(result[goal.X, goal.Y, 1] == 0) result[goal.X, goal.Y, 1] = int.MaxValue;
                Console.WriteLine(Math.Min(result[goal.X, goal.Y, 0], result[goal.X, goal.Y, 1]) - 1);
            }
            Console.ReadLine();
        }

        public class Stat{
            public Stat(int x, int y, int type){
                X = x;
                Y = y;
                Type = type;
            }

            public int X { get; }
            public int Y { get; }
            public int Type { get; }
        }

        public class Point{
            public Point(int x, int y){
                X = x;
                Y = y;
            }

            public int X { get; }
            public int Y { get; }
        }
    }
}