import java.util.Arrays;
import java.util.LinkedList;
import java.util.Scanner;

public class Main {
	
	public static long MOD = 1000000007;
	
	public static final int INF = Integer.MAX_VALUE / 2 - 1;
	public static boolean in_range(int x, int y, int W, int H){
		return 0 <= x && x < W && 0 <= y && y < H;
	}
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		final int H = sc.nextInt();
		final int W = sc.nextInt();
		
		int sx = -1, sy = -1, gx = -1, gy = -1;
		
		boolean[][] is_red = new boolean[H][W];
		for(int i = 0; i < H; i++){
			final char[] ins = sc.next().toCharArray();
			
			for(int j = 0; j < W; j++){
				if(ins[j] == 'R'){
					is_red[i][j] = true;
				}else if(ins[j] == 'S'){
					sx = j; sy = i;
				}else if(ins[j] == 'G'){
					gx = j; gy = i;
				}
			}
		}
		
		LinkedList<Integer> queue = new LinkedList<Integer>();
		final int KNIGHT = 0, MINB = 1;
		int[][][] costs = new int[H][W][2];
		for(int i = 0; i < H; i++){
			for(int j = 0; j < W; j++){
				costs[i][j][0] = INF;
				costs[i][j][1] = INF;
			}
		}	
		costs[sy][sx][KNIGHT] = 0;
		queue.add(sx); queue.add(sy); queue.add(KNIGHT);
		
		while(!queue.isEmpty()){
			final int x = queue.poll();
			final int y = queue.poll();
			final int type = queue.poll();
			//System.out.println(x + " " + y + " " + (type == KNIGHT ? "N" : "B"));
			
			if(type == MINB){
				for(int dy = -1; dy <= 1; dy++){
					for(int dx = -1; dx <= 1; dx++){
						if(dx == 0 && dy == 0){ continue; }
						if(Math.abs(dx) == 0 || Math.abs(dy) == 0){ continue; }
						
						final int nx = x + dx;
						final int ny = y + dy;
						if(!in_range(nx, ny, W, H)){ continue; }
						
						final int next_type = is_red[ny][nx] ? 1 - type : type;
						
						if(costs[ny][nx][next_type] <= costs[y][x][type] + 1){ continue; }
						
						costs[ny][nx][next_type] = costs[y][x][type] + 1;
						queue.add(nx); queue.add(ny); queue.add(next_type);
					}
				}
			}else{
				for(int dy = -2; dy <= 2; dy++){
					for(int dx = -2; dx <= 2; dx++){
						if(Math.abs(dx) == Math.abs(dy)){ continue; }
						if(Math.min(Math.abs(dx), Math.abs(dy)) == 0){ continue; }
						
						final int nx = x + dx;
						final int ny = y + dy;
						if(!in_range(nx, ny, W, H)){ continue; }
						
						final int next_type = is_red[ny][nx] ? 1 - type : type;
						
						if(costs[ny][nx][next_type] <= costs[y][x][type] + 1){ continue; }
						
						costs[ny][nx][next_type] = costs[y][x][type] + 1;
						queue.add(nx); queue.add(ny); queue.add(next_type);
					}
				}
			}
		}
		
		final int min_cost = Math.min(costs[gy][gx][KNIGHT], costs[gy][gx][MINB]);
		
		System.out.println(min_cost >= INF ? -1 : min_cost);
	}
}