/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2020.05.30 18:52:06
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;

int main() {
    int h,w;cin >> h >> w;
    vector<string> g(h);
    int sx,sy,gx,gy;
    for (int i = 0; i < h; i++) {
        cin >> g[i];
        for (int j = 0; j < w; j++) {
            if (g[i][j] == 'S') {
                sx = i;
                sy = j;
            }
            else if (g[i][j] == 'G') {
                gx = i;
                gy = j;
            }
        }
    }
    int k_dx[] = {-2,-1,1,2,2,1,-1,-2},k_dy[] = {1,2,2,1,-1,-2,-2,-1};
    int b_dx[] = {-1,1,1,-1}, b_dy[] = {1,1,-1,-1};
    constexpr int INF = 1e9 + 6;
    vector<vector<vector<int>>> dist(h,vector<vector<int>>(w,vector<int>(2,INF)));
    queue<tuple<int,int,int>> que;
    que.push(make_tuple(sx,sy,0));
    dist[sx][sy][0] = 0;
    while(!que.empty()) {
        auto p = que.front(); que.pop();
        int nx = get<0>(p);
        int ny = get<1>(p);
        int t = get<2>(p);
        if (t == 0) {
            for (int k = 0; k < 8; k++) {
                int x = nx + k_dx[k], y = ny + k_dy[k];
                if (x >= 0 && x < h && y >= 0 && y < w) {
                    if (g[x][y] == 'R' && dist[x][y][1] == INF) {
                        dist[x][y][1] = dist[nx][ny][0] + 1;
                        que.push(make_tuple(x,y,1));
                    }
                    else if (g[x][y] != 'R' && dist[x][y][0] == INF) {
                        dist[x][y][0] = dist[nx][ny][0] + 1;
                        que.push(make_tuple(x,y,0));
                    }
                }
            }
        }
        else {
            for (int k = 0; k < 4; k++) {
                int x = nx + b_dx[k], y = ny + b_dy[k];
                if (x >= 0 && x < h && y >= 0 && y < w) {
                    if (g[x][y] == 'R' && dist[x][y][0] == INF) {
                        dist[x][y][0] = dist[nx][ny][1] + 1;
                        que.push(make_tuple(x,y,0));
                    }
                    else if (g[x][y] != 'R' && dist[x][y][1] == INF) {
                        dist[x][y][1] = dist[nx][ny][1] + 1;
                        que.push(make_tuple(x,y,1));
                    }
                }
            }
        }
    }
    int ans = min(dist[gx][gy][0],dist[gx][gy][1]);
    if (ans == INF) {
        cout << -1 << endl;
    }
    else {
        cout << ans << endl;
    }
    return 0;
}