#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<tuple>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = 1000000007;
const ll INF = (ll)1000000007 * 1000000007;
typedef pair<int, int> P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define Per(i,sta,n) for(int i=n-1;i>=sta;i--)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef long double ld;
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<ll, ll> LP;
typedef pair<int,P> PP;
typedef pair<int,PP> PPP;
vector<int> dx={1,1,-1,-1};
vector<int> dy={1,-1,1,-1};

void solve(){
  int h,w;
  cin >> h >> w;
  vector<string> s(h);
  vector<vector<vector<int>>> d(2,vector<vector<int>>(h,vector<int>(w,mod)));
  vector<vector<vector<bool>>> visited(2,vector<vector<bool>>(h,vector<bool>(w,false)));
  int sx,sy,gx,gy;
  rep(i,h){
    cin >> s[i];
    rep(j,w){
      if(s[i][j]=='S'){
        sy=i;sx=j;
      }
      if(s[i][j]=='G'){
        gy=i,gx=j;
      }
    }
  }
  queue<PPP> que;
  que.push(PPP(0,PP(0,P(sy,sx))));
  d[0][sy][sx]=0;visited[0][sy][sx]=true;
  while(!que.empty()){
    PPP ppp=que.front();que.pop();
    int k=ppp.first,q=ppp.second.first,y=ppp.second.second.first,x=ppp.second.second.second;
    //cout << q << " " << y << " " << x << " " << k << endl;
    rep(i,4){
      if(q==0){
        int ny=y+2*dy[i],nx=x+dx[i];
        if(ny<h && ny>=0 && nx<w && nx>=0){
          int nq=(s[ny][nx]=='R');
          if(visited[nq][ny][nx]) continue;
          d[nq][ny][nx]=k+1;
          visited[nq][ny][nx]=true;
          que.push(PPP(k+1,PP(nq,P(ny,nx))));
        }
        ny=y+dy[i],nx=x+2*dx[i];
        if(ny<h && ny>=0 && nx<w && nx>=0){
          int nq=(s[ny][nx]=='R');
          if(visited[nq][ny][nx]) continue;
          d[nq][ny][nx]=k+1;
          visited[nq][ny][nx]=true;
          que.push(PPP(k+1,PP(nq,P(ny,nx))));
        }
      }
      if(q==1){
        int ny=y+dy[i],nx=x+dx[i];
        if(ny<h && ny>=0 && nx<w && nx>=0){
          int nq=1-(s[ny][nx]=='R');
          if(visited[nq][ny][nx]) continue;
          d[nq][ny][nx]=k+1;
          visited[nq][ny][nx]=true;
          que.push(PPP(k+1,PP(nq,P(ny,nx))));
        }
      }
    }
  }
  
  if(visited[0][gy][gx] || visited[1][gy][gx]){
    cout << min(d[0][gy][gx],d[1][gy][gx]) << endl;
  }
  else{
    cout << -1 << endl;
  }
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(50);
    solve();
}