#include<bits/stdc++.h>
using namespace std;

#define int long long
typedef pair<int,int>pint;
typedef vector<int>vint;
typedef vector<pint>vpint;
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
template<class T,class U>inline void chmin(T &t,U f){if(t>f)t=f;}
template<class T,class U>inline void chmax(T &t,U f){if(t<f)t=f;}

int H,W;
char fld[555][555];
int sy,sx,gy,gx;

const int INF=1001001001;
int dist[555][555][2];

vint dx[2];
vint dy[2];
signed main(){
    dx[0]={-2,-1,1,2,-2,-1,1,2};
    dy[0]={-1,-2,-2,-1,1,2,2,1};
    dx[1]={-1,1,-1,1};
    dy[1]={-1,-1,1,1};


    cin>>H>>W;
    rep(i,H)cin>>fld[i];

    rep(i,H)rep(j,W){
        if(fld[i][j]=='S')sy=i,sx=j;
        if(fld[i][j]=='G')gy=i,gx=j;
    }

    fill_n(**dist,555*555*2,INF);
    dist[sy][sx][0]=0;
    queue<tuple<int,int,int>>que;
    que.push(make_tuple(sy,sx,0));
    while(que.size()){
        int y,x,t;
        tie(y,x,t)=que.front();
        que.pop();
        rep(i,dx[t].size()){
            int ny=y+dy[t][i];
            int nx=x+dx[t][i];
            if(ny<0||ny>=H||nx<0||nx>=W)continue;
            int nt=(t+(fld[ny][nx]=='R'))%2;
            if(dist[ny][nx][nt]!=INF)continue;
            dist[ny][nx][nt]=dist[y][x][t]+1;
            que.push(make_tuple(ny,nx,nt));
        }
    }

    int cost=min(dist[gy][gx][0],dist[gy][gx][1]);
    if(cost==INF)cout<<-1<<endl;
    else cout<<cost<<endl;
    return 0;
}