import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Scanner;

public class Yuki367 {
	static Scanner sc = new Scanner(System.in);
	static int[] nX = { -2, -2, -1, -1, 1, 1, 2, 2 };
	static int[] nY = { -1, 1, -2, 2, -2, 2, -1, 1 };
	static int[] bX = { -1, -1, 1, 1 };
	static int[] bY = { -1, 1, -1, 1 };

	public static void main(String[] args) {
		int H, W;
		H = sc.nextInt();
		W = sc.nextInt();
		sc.nextLine();
		boolean[][][] is = new boolean[2][H][W];
		for (int i = 0; i < 2; i++) {
			for (int j = 0; j < H; j++) {
				Arrays.fill(is[i][j], false);
			}
		}
		int[] start = new int[2];
		String[] S = new String[H];
		for (int i = 0; i < H; i++) {
			S[i] = sc.nextLine();
			for (int j = 0; j < W; j++) {
				if (S[i].charAt(j) == 'S') {
					start[0] = j;
					start[1] = i;
				}
			}
		}
		ArrayDeque<Now> q = new ArrayDeque<>();
		q.add(new Now(start[0], start[1], 0, true));
		while (!q.isEmpty()) {
			Now n = q.poll();
			boolean f = n.knightFlag;
			int nowStep = n.step + 1;
			if (f) {
				for (int i = 0; i < nX.length; i++) {
					int x = n.x + nX[i];
					int y = n.y + nY[i];
					if (x < 0 || x >= W)
						continue;
					if (y < 0 || y >= H)
						continue;
					if (is[1][y][x])
						continue;
					is[1][y][x] = true;
					if (S[y].charAt(x) == 'G') {
						System.out.println(nowStep);
						return;
					}
					if (S[y].charAt(x) == 'R') {
						q.add(new Now(x, y, nowStep, !f));
					} else {
						q.add(new Now(x, y, nowStep, f));
					}
				}
			} else {
				for (int i = 0; i < bX.length; i++) {
					int x = n.x + bX[i];
					int y = n.y + bY[i];
					if (x < 0 || x >= W)
						continue;
					if (y < 0 || y >= H)
						continue;
					if (is[0][y][x])
						continue;
					is[0][y][x] = true;
					if (S[y].charAt(x) == 'G') {
						System.out.println(nowStep);
						return;
					}
					if (S[y].charAt(x) == 'R') {
						q.add(new Now(x, y, nowStep, !f));
					} else {
						q.add(new Now(x, y, nowStep, f));
					}
				}
			}
		}
		System.out.println(-1);
	}

	public static class Now {
		int x;
		int y;
		int step;
		boolean knightFlag;

		Now(int x, int y, int step, boolean f) {
			this.x = x;
			this.y = y;
			this.step = step;
			this.knightFlag = f;
		}
	}
}