#include <bits/stdc++.h>

using namespace std;
#define FOR(i,n) for(int i = 0; i < (n); i++)
#define sz(c) ((int)c.size())
#define ten(n) ((int)1e##n)
using ll = long long;

int n, m;
bool in(int x, int y) {
	return x >= 0 && x < n && y >= 0 && y < m;
}

int dx1[] = { 2, 2, 1, 1, -1, -1, -2, -2 };
int dy1[] = { -1, 1, -2, 2, -2, 2, -1, 1 };

int dx2[] = { 1, 1, -1, -1 };
int dy2[] = { 1, -1, 1, -1 };

char t[500][501];
int memo[500][500][2];

int main() {
	cin >> n >> m;
	FOR(i, n) cin >> t[i];


	int sx, sy, gx, gy;
	FOR(i, n) FOR(j, m) {
		if (t[i][j] == 'S') sx = i, sy = j;
		if (t[i][j] == 'G') gx = i, gy = j;
	}
	memset(memo, 0x2f, sizeof(memo));
	memo[sx][sy][0] = 0;
	queue<tuple<int, int, int>> q;
	q.emplace(sx, sy, 0);
	while (!q.empty()) {
		int x, y, c; tie(x, y, c) = q.front(); q.pop();
		int kmax = (c == 0) ? 8 : 4;
		auto dx = (c == 0) ? dx1 : dx2;
		auto dy = (c == 0) ? dy1 : dy2;
		FOR(k, kmax) {
			int nx = x + dx[k], ny = y + dy[k];
			if (!in(nx, ny)) continue;
			int nc = c;
			if (t[nx][ny] == 'R') nc ^= 1;
			if (memo[nx][ny][nc] > memo[x][y][c] + 1) {
				memo[nx][ny][nc] = memo[x][y][c] + 1;;
				q.emplace(nx, ny, nc);
			}
		}
	}

	int ans = min(memo[gx][gy][0], memo[gx][gy][1]);
	if (ans > ten(5)) ans = -1;
	cout << ans << endl;

	return 0;
}