#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <queue>

using namespace std;
using ull = unsigned long long;
using ll = long long;
using lli = long long int;
using ld = long double;
using pa = pair<int,int>;
using ppa = pair<pa,int>;
#define SORT(v, n) sort(v, v+n);
#define ALL(v) v.begin(),v.end()
#define VSORT(v) sort(ALL(v))
#define GRESORT(v) sort(ALL(v),greater<ll>())
#define REVERSE(v) reverse(ALL(v))
#define overlap(v) v.erase(unique(ALL(v)),v.end())
#define debug(x) cout << #x << ": " << x << endl
#define FOR(i,a,b) for(int i = (a); i < (b); i++)
#define rep(i,n) FOR(i,0,n)
#define RFOR(i,a,b) for(int i = (b-1); i >= a; i--)
#define rrep(i,n) RFOR(i,0,n)
#define INF 999999999
#define mins(a,b) a = min(a,b)
#define maxs(a,b) a = max(a,b)

//4近傍
//int dy[]={0, 1, 0, -1};
//int dx[]={1, 0, -1, 0};

//8近傍
//int dy[]={0,0,1,-1,1,1,-1,-1};
//int dx[]={1,-1,0,0,1,-1,1,-1};

//knight
int kdy[] = {-2,-2,-1,-1,1,1,2,2};
int kdx[] = {-1,1,-2,2,-2,2,-1,1};

//bishop
int bdy[] = {1,1,-1,-1};
int bdx[] = {1,-1,1,-1};

ll mod = 1000000007;

bool check(int x, int y, int h, int w){
    return (x < 0 || y < 0 || y >= h || x >= w);
}

void solve() {
    int h,w; cin >> h >> w;
    char c[510][510];
    int sx,sy,gx,gy;
    int d[510][510][2] = {};
    rep(i,h){
        rep(j,w){
            cin >> c[i][j];
            if(c[i][j] == 'S'){
                sy = i; sx = j;
            }
            if(c[i][j] == 'G'){
                gy = i; gx = j;
            }
            d[i][j][0] = INF;
            d[i][j][1] = INF;
        }
    }
    d[sy][sx][0] = 0;
    queue<ppa> q;
    q.push(ppa(pa(sx,sy),0));
    while(!q.empty()){
        ppa p = q.front(); q.pop();
        pa pp = p.first;
        int x = pp.first, y = pp.second, r = p.second;
        //debug(x); debug(y); debug(r);
        if(gx == x && gy == y) break;
        if(r == 0){
            rep(i,8){
                int xx = x + kdx[i];
                int yy = y + kdy[i];
                if(check(xx,yy,h,w)) continue;
                int nr = r ^ (c[yy][xx] == 'R' ? 1 : 0);
                if(d[yy][xx][nr] == INF){
                    d[yy][xx][nr] = d[y][x][r] + 1;
                    q.push(ppa(pa(xx,yy),nr));
                }
            }
        }else{
            rep(i,4){
                int xx = x + bdx[i];
                int yy = y + bdy[i];
                if(check(xx,yy,h,w)) continue;
                int nr = r ^ (c[yy][xx] == 'R' ? 1 : 0);
                if(d[yy][xx][nr] == INF){
                    d[yy][xx][nr] = d[y][x][r] + 1;
                    q.push(ppa(pa(xx,yy),nr));
                }
            }
        }
    }
    cout << (d[gy][gx][0] != INF || d[gy][gx][1] != INF ? min(d[gy][gx][0],d[gy][gx][1]) : -1) << endl;
}

int main(){
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    solve();

    return 0;
}