#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
using namespace std;

#define RREP(i,s,e) for (i = s; i >= e; i--)
#define rrep(i,n) RREP(i,n-1,0)
#define REP(i,s,e) for (i = s; i < e; i++)
#define rep(i,n) REP(i,0,n)
#define INF 100000000

typedef long long ll;

int main() {
    int i, j, k, l, h, w;
    int dis[2][500][500];
    string s[500];
    cin >> h >> w;
    rep (i,h) cin >> s[i];
    rep (i,2) rep (j,h) rep (k,w) dis[i][j][k] = INF;
    rep (i,h) rep (j,w) if (s[i][j] == 'S') {
        queue<tuple<int,int,int>> q;
        int kn[8] = {2,1,2,-1,-2,1,-2,-1};
        dis[1][i][j] = 0;
        q.push(make_tuple(i,j,true));
        while (!q.empty()) {
            int x, y, d;
            bool knight;
            tie(x,y,knight) = q.front();
            q.pop();
            if (s[x][y] == 'G') {
                cout << dis[knight][x][y] << endl;
                return 0;
            }
            d = dis[knight][x][y];
            knight ^= s[x][y] == 'R';
            if (knight) {
                rep (k,8) {
                    int nx = x+kn[k];
                    int ny = y+kn[(k+1)%8];
                    if (nx >= 0 && nx < h && ny >= 0 && ny < w && dis[knight][nx][ny] > d+1) {
                        dis[knight][nx][ny] = d+1;
                        q.push(make_tuple(nx,ny,knight));
                    }
                }
            }
            else {
                for (k = -1; k <= 1; k+=2) {
                    for (l = -1; l <= 1; l+=2) {
                        int nx = x+k;
                        int ny = y+l;
                        if (nx >= 0 && nx < h && ny >= 0 && ny < w && dis[knight][nx][ny] > d+1) {
                            dis[knight][nx][ny] = d+1;
                            q.push(make_tuple(nx,ny,knight));
                        }
                    }
                }
            }
        }
    }
    cout << -1 << endl;
    return 0;
}