#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

vector<vector<int> > dy = { { 2 ,2,-2,-2, 1, 1,-1,-1}, { 1, 1,-1,-1} };
vector<vector<int> > dx = { { 1,-1, 1,-1, 2,-2, 2,-2}, { 1,-1, 1,-1} };

int main()
{
    int h, w;
    cin >> h >> w;
    vector<string> s(h, string(w, ' '));
    int sy, sx, gy, gx;
    for(int y=0; y<h; ++y){
        for(int x=0; x<w; ++x){
            cin >> s[y][x];
            if(s[y][x] == 'S'){
                sy = y;
                sx = x;
            }
            else if(s[y][x] == 'G'){
                gy = y;
                gx = x;
            }
        }
    }

    vector<vector<vector<bool> > > check(2, vector<vector<bool> >(h, vector<bool>(w, false)));
    queue<tuple<int, int, int> > q;
    check[0][sy][sx] = true;
    q.push(make_tuple(0, sy, sx));
    int ans = 0;
    while(!q.empty()){
        int n = q.size();
        while(--n >= 0){
            int a, y, x;
            tie(a, y, x) = q.front();
            q.pop();

            if(y == gy && x == gx){
                cout << ans << endl;
                return 0;
            }

            for(unsigned i=0; i<dy[a].size(); ++i){
                int y2 = y + dy[a][i];
                int x2 = x + dx[a][i];
                if(!(0 <= y2 && y2 < h && 0 <= x2 && x2 < w))
                    continue;

                int a2;
                if(s[y2][x2] == 'R')
                    a2 = a ^ 1;
                else
                    a2 = a;

                if(!check[a2][y2][x2]){
                    check[a2][y2][x2] = true;
                    q.push(make_tuple(a2, y2, x2));
                }
            }
        }
        ++ ans;
    }

    cout << -1 << endl;
    return 0;
}