#include <iostream>
#include <queue>
#include <string>
#include <map>

const int INF = 10000000;

using namespace std;

typedef pair<int,int> P;
int ary[550][550];

int nxmove[8] = {1,-1,1,-1,2,-2,2,-2};
int nymove[8] = {2,2,-2,-2,1,1,-1,-1};

int bxmove[4] = {1,-1,1,-1};
int bymove[4] = {1,1,-1,-1};

int sx ,sy,gx,gy;

int h,w;
string str[1010];

bool koma = 1;

int bfs()
{
	queue<P> que;

	for(int i=0; i<h; i++)
		for(int j=0; j<w; j++)

			ary[i][j] = INF;

			que.push(P(sx,sy));
			ary[sy][sx] = 0;

			while(!que.empty())
			{
				P p = que.front();
				que.pop();

				int x = p.first;
				int y = p.second;

				if(x == gx && y == gy)
					break;

					if(str[y][x] == 'R'){
						if(str[y][x] == 'R' && koma == 1)
						{
							for(int i=0; i<8; i++)
						{

							int mx = x + nxmove[i];
							int my = y + nymove[i];

							if(mx < 0 || my < 0 || mx >= w || my >= h)
							continue;

							if(INF == ary[my][mx])
							que.push(P(mx,my));
							if(koma == 1){
							ary[my][mx] = ary[y][x] + 1;
							koma = 0;
								}
							}
						}
					for(int i = 0; i < 4; i++)
					{
							int mx = x + bxmove[i];
							int my = y + bymove[i];

							if(mx < 0 || my < 0 || mx >= w || my >= h)
							continue;

						if(INF == ary[my][mx])
							que.push(P(mx,my));
						if(koma == 0){
							ary[my][mx] = ary[y][x] + 1;
							koma = 1;
						}
					}
				}

				for(int i=0; i<8; i++)
				{

						int mx = x + nxmove[i];
						int my = y + nymove[i];

					if(mx < 0 || my < 0 || mx >= w || my >= h)
						continue;

					if(INF == ary[my][mx])
						que.push(P(mx,my));
						ary[my][mx] = ary[y][x] + 1;
				}

		}
		return ary[gy][gx];
}

int main()
{
	cin >> h >> w;

	for(int i = 0; i < h; i++)
	{
		cin >> str[i];

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

	int ans = bfs();

	if(ans != INF)
	cout << ans << endl;

	else
		cout << -1 << endl;

	return 0;
}