#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef complex<double> P;
typedef pair<int,int> pii;
#define REP(i,n) for(ll i=0;i<n;++i)
#define REPR(i,n) for(ll i=1;i<n;++i)
#define FOR(i,a,b) for(ll i=a;i<b;++i)

#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define DEBUG_VEC(v) cout<<#v<<":";REP(i,v.size())cout<<" "<<v[i];cout<<endl
#define ALL(a) (a).begin(),(a).end()

#define MOD (ll)(1e9+7)
#define ADD(a,b) a=((a)+(b))%MOD
#define FIX(a) ((a)%MOD+MOD)%MOD

const int INF = 830252521;

int h,w;
bool mp[525][525];
int sy,sx,gy,gx;
// NorB, y, x
int dp[2][525][525];

int dxn[] = {2,2,1,1,-1,-1,-2,-2};
int dyn[] = {1,-1,2,-2,2,-2,1,-1};

int dxb[] = {1,1,-1,-1};
int dyb[] = {1,-1,1,-1};

struct state{
  int y,x,id;
  state(int y,int x,int id):y(y),x(x),id(id){}
};

int main(){
  scanf("%d%d",&h,&w);
  REP(i,h){
    char s[525];
    scanf("%s",s);
    REP(j,w){
      mp[i][j] = (s[j]=='R');
      if(s[j]=='S'){
        sy=i;
        sx=j;
      }else if(s[j]=='G'){
        gy=i;
        gx=j;
      }
    }
  }
  REP(x,2)REP(i,h)REP(j,w)dp[x][i][j]=INF;
  dp[0][sy][sx] = 0;
  queue<state> Q;
  Q.push(state(sy,sx,0));
  while(!Q.empty()){
    state S = Q.front(); Q.pop();
    int id = S.id, y = S.y, x = S.x;
    // DEBUG(x);
    // DEBUG(y);
    // DEBUG(id);
    int d = dp[id][y][x];
    REP(i,(id?4:8)){
      int ny = y+(id?dyb[i]:dyn[i]);
      int nx = x+(id?dxb[i]:dxn[i]);
      if(ny<0 || nx<0 || ny>=h || nx>=w)continue;
      if(mp[ny][nx]){
        if(dp[1-id][ny][nx]!=INF)continue;
        dp[1-id][ny][nx] = d+1;
        Q.push(state(ny,nx,1-id));
      }else{
        if(dp[id][ny][nx]!=INF)continue;
        dp[id][ny][nx] = d+1;
        Q.push(state(ny,nx,id));
      }
    }
  }
  // REP(x,2){
  //   REP(i,h){
  //     REP(j,w)printf("%10d",dp[x][i][j]);
  //     printf("\n");
  //   }
  //   printf("\n");
  // }
  int ans = min(dp[0][gy][gx],dp[1][gy][gx]);
  if(ans==INF)ans=-1;
  printf("%d\n",ans);
  return 0;
}