import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

public class Main2 {
    static int h,w;
    static char list[][];
    static int dp[][][];
    static int goalX, goalY;
    
    static final int NIGHT = 0;
    static final int BISHOP = 1;
    static int nDirX[] = { 1,  1, -1, -1, 2,  2, -2, -2 };
    static int nDirY[] = { 2, -2,  2, -2, 1, -1,  1, -1 };
    static int bDirX[] = { 1,  1, -1, -1 };
    static int bDirY[] = { 1, -1,  1, -1 };
    
    public static void main(String[] args) {
        try (Scanner scan = new Scanner(System.in)) {
            h = Integer.parseInt(scan.next());
            w = Integer.parseInt(scan.next());
            list = new char[h][w];
            dp = new int[h][w][2];
            int startX = 0, startY = 0;
            
            for(int i=0; i<h; i++) {
                String line = scan.next();
                for(int j=0; j<w; j++) {
                    char ch = line.charAt(j);
                    list[i][j] = ch;
                    if(ch == 'G') {
                        goalX = j;
                        goalY = i;
                    } else if(ch == 'S') {
                        startX = j;
                        startY = i;
                    }
                    
                    for(int k=0; k<2; k++) {
                        dp[i][j][k] = Integer.MAX_VALUE;
                    }
                }   
            }
            solve(startX, startY);
            System.out.println(-1);
        }
    }
    
    static void solve(int startX, int startY) {
        
        Queue<Node> q = new LinkedList<>();
        Node s = new Node(startX, startY, 0, NIGHT);
        q.add(s);
        
        while(!q.isEmpty()) {
            
            Node now = q.poll();
            
            if(now.x == goalX && now.y == goalY) {
                System.out.println(now.steps);
                System.exit(0);
            }
            
            if(now.state == NIGHT) {
                if(dp[now.y][now.x][NIGHT] > now.steps) {
                    dp[now.y][now.x][NIGHT] = now.steps;
                } else {           
                    continue;
                }
            } else {
                if(dp[now.y][now.x][BISHOP] > now.steps) {
                    dp[now.y][now.x][BISHOP] = now.steps;
                } else {           
                    continue;
                }
            }
            
            if(now.state == NIGHT) {
              
                for(int i=0; i<8; i++) {
                    int nextX = now.x + nDirX[i];
                    int nextY = now.y + nDirY[i];
                    
                    if(nextX >= 0 && nextX <= w-1 && nextY >= 0 && nextY <= h-1 ) {
                      
                        int nextState = now.state;
                        if(list[nextY][nextX] == 'R') {
                            nextState = BISHOP;
                        }
                      
                        Node next = new Node(nextX, nextY, now.steps+1, nextState);
                        q.add(next);
                    }
                }
              
            } else if(now.state == BISHOP) {
              
                for(int i=0; i<4; i++) {
                    int nextX = now.x + bDirX[i];
                    int nextY = now.y + bDirY[i];
                    
                    if(nextX >= 0 && nextX <= w-1 && nextY >= 0 && nextY <= h-1 ) {
                      
                        int nextState = now.state;
                        if(list[nextY][nextX] == 'R') {
                            nextState = NIGHT;
                        }
                      
                        Node next = new Node(nextX, nextY, now.steps+1, nextState);
                        q.add(next);
                    }
                }
            }
        }
    }
}

class Node {
    int x, y;
    int steps;
    int state;
    Node(int x, int y, int steps, int state) {
        this.x = x;
        this.y = y;
        this.steps = steps;;
        this.state = state;
    }
}