package yukicoder;
import java.util.ArrayDeque;
import java.util.Scanner;
public class Main{
	public static void main(String[] args)throws Exception{
		new Main().solve();
	}
	void solve(){
		Scanner sc=new Scanner(System.in);
		int h=sc.nextInt();
		int w=sc.nextInt();
		int sx=-1,sy=-1;
		char[][] table=new char[h][w];
		for(int i=0;i<h;i++){
			table[i]=sc.next().toCharArray();
			for(int j=0;j<w;j++){
				char c=table[i][j];
				if(c=='S'){
					sx=j;
					sy=i;
				}
			}
		}
		boolean[][] arrived_Knight=new boolean[h][w];
		boolean[][] arrived_Bishop=new boolean[h][w];
		arrived_Knight[sy][sx]=true;
		ArrayDeque<P> que=new ArrayDeque<P>();
		que.add(new P(sx,sy,"Knight",0));
		while(!que.isEmpty()){
			P p=que.poll();
			if(table[p.y][p.x]=='G'){
				System.out.println(p.n);
				return;
			}else if(p.state.equals("Knight")){
				arrived_Knight[p.y][p.x]=true;
				for(int i=0;i<8;i++){
					int nx=p.x+dx1[i];
					int ny=p.y+dy1[i];
					if(nx<0||ny<0||nx>=w||ny>=h)continue;
					if(arrived_Knight[ny][nx])continue;
					if(table[ny][nx]=='R'){
						que.add(new P(nx,ny,"Bishop",p.n+1));
					}else{
						que.add(new P(nx,ny,"Knight",p.n+1));
					}
				}
			}else if(p.state.equals("Bishop")){
				arrived_Bishop[p.y][p.x]=true;
				for(int i=0;i<4;i++){
					int nx=p.x+dx2[i];
					int ny=p.y+dy2[i];
					if(nx<0||ny<0||nx>=w||ny>=h)continue;
					if(arrived_Bishop[ny][nx])continue;
					if(table[ny][nx]=='R'){
						que.add(new P(nx,ny,"Knight",p.n+1));
					}else{
						que.add(new P(nx,ny,"Bishop",p.n+1));
					}
				}
			}
		}
		System.out.println(-1);
	}

	final int[] dx1={1,1,-1,-1,2,2,-2,-2};
	final int[] dy1={2,-2,2,-2,1,-1,1,-1};
	final int[] dx2={1,1,-1,-1};
	final int[] dy2={1,-1,1,-1};

	class P{
		int x;
		int y;
		String state;//Knight,Bishop
		int n;
		P(int x,int y,String state,int n){
			this.x=x;
			this.y=y;
			this.state=state;
			this.n=n;
		}
	}
}