package contest;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.InputMismatchException;
import java.util.Queue;

public class Q996 {
	InputStream is;
	PrintWriter out;
	String INPUT = "";
	
	static int[] DRK = {-2,-2,-1,-1,1,1,2,2};
	static int[] DCK = {-1,1,-2,2,-2,2,-1,1};
	static int[] DR4 = {-1,1,1,-1};
	static int[] DC4 = {1,-1,1,-1};
	
	void solve()
	{
		int n = ni(), m = ni();
		char[][] map = nm(n,m);
		int sr = -1, sc = -1;
		int gr = -1, gc = -1;
		for(int i= 0;i < n;i++){
			for(int j = 0;j < m;j++){
				if(map[i][j] == 'S'){
					sr = i; sc = j;
					map[sr][sc] = '.';
				}
				if(map[i][j] == 'G'){
					gr = i; gc = j;
					map[gr][gc] = '.';
				}
			}
		}
		
		int[][] dr = {DRK, DR4};
		int[][] dc = {DCK, DC4};
		int[][][] d = new int[2][n][m];
		int I = 999999999;
		for(int i = 0;i < n;i++) {
			Arrays.fill(d[0][i], I);
			Arrays.fill(d[1][i], I);
		}
		
		Queue<int[]> q = new ArrayDeque<int[]>();
		q.add(new int[]{0, sr, sc});
		d[0][sr][sc] = 0;
		
		while(!q.isEmpty()){
			int[] cur = q.poll();
			int t = cur[0], r = cur[1], c = cur[2];
			for(int k = 0;k < dr[t].length;k++) {
				int nr = r + dr[t][k];
				int nc = c + dc[t][k];
				if(nr >= 0 && nr < n && nc >= 0 && nc < m){
					int nt = t;
					if(map[nr][nc] == 'R'){
						nt ^= 1;
					}
					if(d[nt][nr][nc] == I) { // fix
						d[nt][nr][nc] = d[t][r][c] + 1;
						q.add(new int[]{nt, nr, nc});
					}
				}
			}
		}
		int ret = Math.min(d[0][gr][gc], d[1][gr][gc]);
		if(ret >= I){
			out.println(-1);
		}else{
			out.println(ret);
		}
	}
	
	
	void run() throws Exception
	{
		is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
		out = new PrintWriter(System.out);
		
		long s = System.currentTimeMillis();
		solve();
		out.flush();
		if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
	}
	
	public static void main(String[] args) throws Exception { new Q996().run(); }
	
	private byte[] inbuf = new byte[1024];
	private int lenbuf = 0, ptrbuf = 0;
	
	private int readByte()
	{
		if(lenbuf == -1)throw new InputMismatchException();
		if(ptrbuf >= lenbuf){
			ptrbuf = 0;
			try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); }
			if(lenbuf <= 0)return -1;
		}
		return inbuf[ptrbuf++];
	}
	
	private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
	private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }
	
	private double nd() { return Double.parseDouble(ns()); }
	private char nc() { return (char)skip(); }
	
	private String ns()
	{
		int b = skip();
		StringBuilder sb = new StringBuilder();
		while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ')
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}
	
	private char[] ns(int n)
	{
		char[] buf = new char[n];
		int b = skip(), p = 0;
		while(p < n && !(isSpaceChar(b))){
			buf[p++] = (char)b;
			b = readByte();
		}
		return n == p ? buf : Arrays.copyOf(buf, p);
	}
	
	private char[][] nm(int n, int m)
	{
		char[][] map = new char[n][];
		for(int i = 0;i < n;i++)map[i] = ns(m);
		return map;
	}
	
	private int[] na(int n)
	{
		int[] a = new int[n];
		for(int i = 0;i < n;i++)a[i] = ni();
		return a;
	}
	
	private int ni()
	{
		int num = 0, b;
		boolean minus = false;
		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
		if(b == '-'){
			minus = true;
			b = readByte();
		}
		
		while(true){
			if(b >= '0' && b <= '9'){
				num = num * 10 + (b - '0');
			}else{
				return minus ? -num : num;
			}
			b = readByte();
		}
	}
	
	private long nl()
	{
		long num = 0;
		int b;
		boolean minus = false;
		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
		if(b == '-'){
			minus = true;
			b = readByte();
		}
		
		while(true){
			if(b >= '0' && b <= '9'){
				num = num * 10 + (b - '0');
			}else{
				return minus ? -num : num;
			}
			b = readByte();
		}
	}
	
	private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); }
}