#include <bits/stdc++.h>
#define EPS 1e-9
#define INF 1070000000LL
#define MOD 1000000007LL
#define fir first
#define foreach(it,X) for(auto it=(X).begin();it!=(X).end();it++)
#define numa(x,a) for(auto x: a)
#define ite iterator
#define mp make_pair
#define rep(i,n) rep2(i,0,n)
#define rep2(i,m,n) for(int i=m;i<(n);i++)
#define pb push_back
#define pf push_front
#define sec second
#define sz(x) ((int)(x).size())
#define ALL( c ) (c).begin(), (c).end()
#define gcd(a,b) __gcd(a,b)
#define mem(x,n) memset(x,n,sizeof(x))
#define endl "\n"
using namespace std;
template <int POS, class TUPLE> void deploy(std::ostream &os, const TUPLE &tuple){}
template <int POS, class TUPLE, class H, class ...Ts> void deploy(std::ostream &os, const TUPLE &t){ os << (POS == 0 ? "" : ", ") << get<POS>(t); deploy<POS + 1, TUPLE, Ts...>(os, t); }
template <class T,class U> std::ostream& operator<<(std::ostream &os, std::pair<T,U> &p){ os << "(" << p.first <<", " << p.second <<")";return os; }
template <class T> std::ostream& operator<<(std::ostream &os, std::vector<T> &v){ int remain = v.size(); os << "{"; for(auto e: v) os << e << (--remain == 0 ? "}" : ", "); return os; }
template <class T> std::ostream& operator<<(std::ostream &os, std::set<T> &v){ int remain = v.size(); os << "{"; for(auto e: v) os << e << (--remain == 0 ? "}" : ", "); return os; }
template <class T, class K> std::ostream& operator<<(std::ostream &os, std::map<T, K> &mp){ int remain = mp.size(); os << "{"; for(auto e: mp) os << "(" << e.first << " -> " << e.second << ")" << (--remain == 0 ? "}" : ", "); return os; }
#define DEBUG1(var0) { std::cerr << (#var0) << "=" << (var0) << endl; }
#define DEBUG2(var0, var1) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG1(var1); }
#define DEBUG3(var0, var1, var2) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG2(var1,var2); }
#define DEBUG4(var0, var1, var2, var3) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG3(var1,var2,var3); }
using ll = long long;

int H,W;
string bd[510];
int memo[510][510][2];
int sx, sy;
int gx, gy;
int main()
{
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  mem(memo,-1);
  cin >> H >> W;
  rep(i,H){
    cin >> bd[i];
    auto j = bd[i].find('G');
    auto j2 = bd[i].find('S');
    if (j != string::npos) {
      gx = i;
      gy = j;
    }
    if (j2 != string::npos) {
      sx = i;
      sy = j2;
    }
  }
  vector <int> dxkn = {-2, -2, -1, -1, 1, 1, 2, 2};
  vector <int> dykn = {-1, 1, -2, 2, -2, 2, -1, 1};
  vector <int> dxvi = {-1,-1,1,1};
  vector <int> dyvi = {-1,1,-1,1};
  using T = pair <bool, pair <int,int> >;
  queue <T> que;
  memo[sx][sy][true]= 0;
  que.push(mp(true, mp(sx, sy)));
  while (!que.empty()) {
    auto t = que.front();
    que.pop();
    bool kn = t.fir;
    int x = t.sec.fir;
    int y = t.sec.sec;
    int c = memo[x][y][kn];
    if (bd[x][y] == 'R') {
      kn = !kn;
    }
    vector <int> &dx = kn ? dxkn : dxvi;
    vector <int> &dy = kn ? dykn : dyvi;
    for (int k = 0; k < sz(dx); k++) {
      int nx = x + dx[k];
      int ny = y + dy[k];
      if (0 <= nx && nx < H && 0 <= ny && ny < W) {
        if (memo[nx][ny][kn] == -1) {
          memo[nx][ny][kn] = c + 1;
          que.push(mp(kn, mp(nx,ny)));
        }
      }
    }
  }
  int ans1 = memo[gx][gy][0];
  int ans2 = memo[gx][gy][1];
  int ans = INF;
  if (ans1 >= 0) {
    ans = min(ans,ans1);
  }
  if (ans2 >= 0) {
    ans = min(ans,ans2);
  }
  if (ans == INF) {
    cout << -1 << endl;
  }else{
    cout << ans << endl;
  }
  return 0;
}