#include <bits/stdc++.h>
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define FORR(i,a,b) for (int i=(a);i>=(b);i--)
#define pb push_back
#define pcnt __builtin_popcount
#define show(x) cout<<#x<<" = "<<x<<endl;
#define maxs(x,y) x = max(x,y)
#define mins(x,y) x = min(x,y)
#define fi first
#define se second
#define rng(a) a.begin(),a.end()
#define each(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define sz(x) (int)(x).size()
#define mp make_pair

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vpii;
typedef set<int> si;
typedef pair<ll,ll> pll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<pll> vpll;
typedef set<ll> sl;
template<typename T>string join(vector<T>&v)
{stringstream s;FOR(i,0,sz(v))s<<' '<<v[i];return s.str().substr(1);}
ll gcd(ll a,ll b){if(a>b)swap(a,b);for(;a>0;b%=a,swap(a,b));return b;}
int modpow(ll a,ll n,int m){if(a==0)return a;ll p=1;for(;n>0;n/=2,a=a*a%m)if(n&1)p=p*a%m;return(int)p;}
void dout(double d){printf("%.12f\n",d);}

const int iinf = 1e9;
const ll linf = 1e18;
const int mod = 1e9+7;
const double pi = acos(-1);
const double eps = 1e-10;
int h, w, red[500][500];
pii g;
bool y[2][500][500];
queue<pair<int, pii> > q, q2;
pair<int, pii> t;
vpii v[2];

main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  for(int j = -1; j < 2; j += 2)for(int k = -1; k < 2; k += 2){
    FOR(i, 1, 3) v[0].pb(mp(i*j, (3-i)*k));
    v[1].pb(mp(j, k));
  }
  cin >> h >> w;
  FOR(i, 0, h){
    string s;
    cin >> s;
    FOR(j, 0, w){
      switch(s[j]){
        case 'R':
          red[i][j] = 1;
          break;
        case 'S':
          q.push(mp(0, mp(i, j)));
          y[0][i][j] = true;
          break;
        case 'G':
          g = mp(i, j);
          break;
        default:
          break;
      }
    }
  }
  int cnt = 0, _h, _w, _r;
  while(!q.empty()){
    while(!q.empty()){
      t = q.front();
      q.pop();
      if(t.se == g){
        cout << cnt << endl;
        return 0;
      }
      each(itr, v[t.fi]){
        _h = t.se.fi + itr->fi;
        _w = t.se.se + itr->se;
        if(0<=_h && _h<h && 0<=_w && _w<w){
          _r = t.fi ^ red[_h][_w];
          if(!y[_r][_h][_w]){
            y[_r][_h][_w] = true;
            q2.push(mp(_r, mp(_h, _w)));
          }
        }
      }
    }
    cnt++;
    swap(q, q2);
  }
  cout << -1 << endl;
  return 0;
}