#include <bits/stdc++.h>

using namespace std;

int H, W;
int dist[501][501][2];
char board[501][501];
int dy0[8] = { -1,-2,-2,-1,1,2,2,1 };
int dx0[8] = { -2,-1,1,2,2,1,-1,-2 };
int dy1[4] = { -1,-1,1,1 };
int dx1[4] = { -1,1,1,-1 };

int main(void)
{
	cin.tie(0);
	ios::sync_with_stdio(false);

	int gy = -1;
	int gx = -1;
	int sy = -1;
	int sx = -1;

	cin >> H >> W;

	for (int i = 0; i < H; i++)
	{
		for (int j = 0; j < W; j++)
		{
			cin >> board[i][j];
			if (board[i][j] == 'S')
			{
				sy = i;
				sx = j;
			}
			else if (board[i][j] == 'G')
			{
				gy = i;
				gx = j;
			}
		}
	}

	for (int i = 0; i < H; i++)
	{
		for (int j = 0; j < W; j++)
		{
			dist[i][j][0] = 1e9;
			dist[i][j][1] = 1e9;
		}
	}

	dist[sy][sx][0] = 0;
	priority_queue <pair<int, pair<pair<int, int>, int>>,vector<pair<int, pair<pair<int, int>, int>>>,greater<pair<int, pair<pair<int, int>, int>>>> pque;
	pque.push(make_pair(dist[sy][sx][0], make_pair(make_pair(sy, sx), 0)));

	while (!pque.empty())
	{
		int y = pque.top().second.first.first;
		int x = pque.top().second.first.second;
		int t = pque.top().second.second;
		if (dist[y][x][t] < pque.top().first)
		{
			pque.pop();
			continue;
		}
		pque.pop();

		if (t == 0)
		{
			for (int k = 0; k < 8; k++)
			{
				int ny = y + dy0[k];
				int nx = x + dx0[k];
				if (ny < 0 || ny >= H || nx < 0 || nx >= W) continue;
				if (board[ny][nx] == 'R')
				{
					if (dist[ny][nx][1] > dist[y][x][0] + 1)
					{
						dist[ny][nx][1] = dist[y][x][0] + 1;
						pque.push(make_pair(dist[ny][nx][1], make_pair(make_pair(ny, nx), 1)));
					}
				}
				else
				{
					if (dist[ny][nx][0] > dist[y][x][0] + 1)
					{
						dist[ny][nx][0] = dist[y][x][0] + 1;
						pque.push(make_pair(dist[ny][nx][0], make_pair(make_pair(ny, nx), 0)));
					}
				}
			}
		}
		else
		{
			for (int k = 0; k < 4; k++)
			{
				int ny = y + dy1[k];
				int nx = x + dx1[k];
				if (ny < 0 || ny >= H || nx < 0 || nx >= W) continue;
				if (board[ny][nx] == 'R')
				{
					if (dist[ny][nx][0] > dist[y][x][1] + 1)
					{
						dist[ny][nx][0] = dist[y][x][1] + 1;
						pque.push(make_pair(dist[ny][nx][0], make_pair(make_pair(ny, nx), 0)));
					}
				}
				else
				{
					if (dist[ny][nx][1] > dist[y][x][1] + 1)
					{
						dist[ny][nx][1] = dist[y][x][1] + 1;
						pque.push(make_pair(dist[ny][nx][1], make_pair(make_pair(ny, nx), 1)));
					}
				}
			}
		}
	}

	int res = min(dist[gy][gx][0], dist[gy][gx][1]);
	if (res >= 1e9) res = -1;

	cout << res << '\n';

	return 0;
}