import java.io.*;
import java.util.*;


public class Main_yukicoder367 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Printer pr = new Printer(System.out);

        int h = sc.nextInt();
        int w = sc.nextInt();
        char[][] ban = new char[h][];
        for (int i = 0; i < h; i++) {
        	ban[i] = sc.next().toCharArray();
        }

        int sx = 0;
        int sy = 0;
        int gx = 0;
        int gy = 0;
        for (int i = 0; i < h; i++) {
        	for (int j = 0; j < w; j++) {
        		if (ban[i][j] == 'S') {
        			sx = j;
        			sy = i;
        		}
        		if (ban[i][j] == 'G') {
        			gx = j;
        			gy = i;
        		}
        	}
        }

        int[] dxn = {2, 2, 1, 1, -1, -1, -2, -2};
        int[] dyn = {1, -1, 2, -2, 2, -2, 1, -1};
        int[] dxb = {1, 1, -1, -1};
        int[] dyb = {1, -1, 1, -1};

        Queue<Integer> qx = new ArrayDeque<>();
        Queue<Integer> qy = new ArrayDeque<>();
        Queue<Integer> qs = new ArrayDeque<>();
        Queue<Integer> qc = new ArrayDeque<>();
        qx.add(sx);
        qy.add(sy);
        qs.add(0);
        qc.add(0);
        boolean[][][] used = new boolean[2][h][w];
        used[0][sy][sx] = true;

        int res = 0;
        while (!qx.isEmpty()) {
        	int x = qx.remove();
        	int y = qy.remove();
        	int s = qs.remove();
        	int cnt = qc.remove();

        	if (x == gx && y == gy) {
        		res = cnt;
        		break;
        	}

        	if (s == 0) {
        		for (int i = 0; i < dxn.length; i++) {
        			int nx = x + dxn[i];
        			int ny = y + dyn[i];
        			int ns = s;

        			if (nx < 0 || nx >= w || ny < 0 || ny >= h) {
        				continue;
        			}

        			if (ban[ny][nx] == 'R') {
        				ns = (s + 1) % 2;
        			}

        			if (used[ns][ny][nx]) {
        				continue;
        			}

        			used[ns][ny][nx] = true;
        			qx.add(nx);
        			qy.add(ny);
        			qs.add(ns);
        			qc.add(cnt + 1);
        		}
        	} else {
        		for (int i = 0; i < dxb.length; i++) {
        			int nx = x + dxb[i];
        			int ny = y + dyb[i];
        			int ns = s;

        			if (nx < 0 || nx >= w || ny < 0 || ny >= h) {
        				continue;
        			}

        			if (ban[ny][nx] == 'R') {
        				ns = (ns + 1) % 2;
        			}

        			if (used[ns][ny][nx]) {
        				continue;
        			}

        			used[ns][ny][nx] = true;
        			qx.add(nx);
        			qy.add(ny);
        			qs.add(ns);
        			qc.add(cnt + 1);
        		}
        	}
        }

        if (res == 0) {
        	pr.println(-1);
        } else {
        	pr.println(res);
        }

        pr.close();
        sc.close();
    }

	@SuppressWarnings("unused")
	private static class Scanner {
		BufferedReader br;
		Iterator<String> it;

		Scanner (InputStream in) {
			br = new BufferedReader(new InputStreamReader(in));
		}

		String next() throws RuntimeException  {
			try {
				if (it == null || !it.hasNext()) {
					it = Arrays.asList(br.readLine().split(" ")).iterator();
				}
				return it.next();
			} catch (IOException e) {
				throw new IllegalStateException();
			}
		}

		int nextInt() throws RuntimeException {
			return Integer.parseInt(next());
		}

		long nextLong() throws RuntimeException {
			return Long.parseLong(next());
		}

		float nextFloat() throws RuntimeException {
			return Float.parseFloat(next());
		}

		double nextDouble() throws RuntimeException {
			return Double.parseDouble(next());
		}

		void close() {
			try {
				br.close();
			} catch (IOException e) {
//				throw new IllegalStateException();
			}
		}
	}

	private static class Printer extends PrintWriter {
		Printer(PrintStream out) {
			super(out);
		}
	}
}