#include <bits/stdc++.h>
using namespace std;
#define all(c) (c).begin(),(c).end()
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;i--)
#define REP(i,m,n) for(int i=(int)(m);i<(int)(n);i++)
#define rep(i,n) REP(i,0,n)
#define iter(c) __typeof((c).begin())
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
#define mem(a) memset(a,0,sizeof(a))
#define pd(a) printf("%.10f\n",a)
#define pb(a) push_back(a)
#define in(a) insert(a)
#define pi M_PI
#define R cin>>
#define F first
#define S second
#define C class
#define ll long long
#define ln cout<<'\n'
#define _(_1,_2,_3,N,...)N
#define pr(...) _(__VA_ARGS__,pr3,pr2,pr1)(__VA_ARGS__)
template<C T>void pr1(T a){cout<<a;ln;}
template<C T,C T2>void pr2(T a,T2 b){cout<<a<<' '<<b;ln;}
template<C T,C T2,C T3>void pr3(T a,T2 b,T3 c){cout<<a<<' '<<b<<' '<<c;ln;}
template<C T>void PR(T a,int n){rep(i,n){if(i)cout<<' ';cout<<a[i];}ln;}
bool check(int n,int m,int x,int y){return x>=0&&x<n&&y>=0&&y<m;}
const ll MAX=1000000007,MAXL=1LL<<60,dx[2][8]={{-1,-2,-2,-1,1,2,2,1},{-1,-1,1,1,0,0,0,0}},dy[2][8]={{-2,-1,1,2,-2,-1,1,2},{-1,1,-1,1,0,0,0,0}};
typedef pair<int,int> P;
typedef pair<int,P> PP;
void Main() {
  int n,m;
  cin >> n >> m;
  string s[n];
  int a[n][m],sx,sy,tx,ty;
  rep(i,n) {
    cin >> s[i];
    rep(j,m) {
      if(s[i][j]=='R') a[i][j]=1;
      else a[i][j]=0;
      if(s[i][j]=='S') sx=i,sy=j;
      if(s[i][j]=='G') tx=i,ty=j;
    }
  }
  int d[2][n][m];
  rep(i,2)rep(j,n)rep(k,m)d[i][j][k]=MAX;
  queue<PP> que;
  que.push(PP(0,P(sx,sy)));
  d[0][sx][sy]=0;
  while(!que.empty()) {
    PP p=que.front();que.pop();
    int nx=p.S.F,ny=p.S.S,t=p.F;
    rep(i,8) {
      int x=nx+dx[t][i],y=ny+dy[t][i];
      if(t&&i>=4) break;
      int tt=t;
      if(!check(n,m,x,y)) continue;
      if(a[x][y]) tt^=1;
      if(d[tt][x][y]!=MAX) continue;
      que.push(PP(tt,P(x,y)));
      d[tt][x][y]=d[t][nx][ny]+1;
    }
  }
  int ans=min(d[0][tx][ty],d[1][tx][ty]);
  if(ans==MAX) pr(-1);
  else pr(ans);
}

int main() {
  ios::sync_with_stdio(0);cin.tie(0);
  Main();return 0;
}