#include<bits/stdc++.h>

using namespace std;
typedef long long int ll;

#define debugv(v) printf("L%d %s => ",__LINE__,#v);for(auto e:v){cout<<e<<" ";}cout<<endl;
#define debugm(m) printf("L%d %s is..\n",__LINE__,#m);for(auto v:m){for(auto e:v){cout<<e<<" ";}cout<<endl;}
#define debuga(m,w) printf("L%d %s is => ",__LINE__,#m);for(int x=0;x<(w);x++){cout<<(m)[x]<<" ";}cout<<endl;
#define debugaa(m,w,h) printf("L%d %s is..\n",__LINE__,#m);for(int y=0;y<(h);y++){for(int x=0;x<(w);x++){cout<<(m)[x][y]<<" ";}cout<<endl;}
#define ALL(v) (v).begin(),(v).end()
#define BIGINT 0x7FFFFFFF
#define E107 1000000007

template<typename T1,typename T2>
ostream& operator <<(ostream &o,const pair<T1,T2> p){o<<"("<<p.first<<":"<<p.second<<")";return o;}

int w,h;
char maze[505][505];
int dp[505][505][2];

int movePatternX[2][9]={{-2,-2,-1,-1, 1, 1, 2, 2,0},{-1,-1, 1, 1, 0, 0, 0, 0,0}};
int movePatternY[2][9]={{-1, 1,-2, 2,-2, 2,-1, 1,0},{-1, 1,-1, 1, 0, 0, 0, 0,0}};

inline bool inmap(int x,int y){
    return 0<=x && x<w && 0<=y && y<h;
}

int main(){
    int i,j,k,l;
    int m,n;
    
    int sx=-1,sy;
    
    cin>>h>>w;cin.ignore();
    
    for (i=0;i<h;i++){
        gets(maze[i]);
        if (sx<0)
            for (j=0;j<w;j++){
                if (maze[i][j]=='S'){
                    sx=j;sy=i;
                    break;
                }
            }
    }
    
    queue<vector<int>> q;
    q.push(vector<int>{0,sx,sy,0});
    dp[sx][sy][0]=1;
    
    int x,y,cnt,job,tx,ty;int ddd=0;
    while (!q.empty()){
        const vector<int> &qfront = q.front();
        cnt=qfront[0]+1;x=qfront[1];y=qfront[2];job=qfront[3];
        q.pop();
        
        if (maze[y][x]=='G'){
            cout<<(cnt-1)<<endl;
            return 0;
        }
        if (maze[y][x]=='R') job=!job;
        
        for (i=0;movePatternX[job][i]!=0;i++){
            tx=x+movePatternX[job][i];
            ty=y+movePatternY[job][i];
            if (inmap(tx,ty) && !dp[tx][ty][job]){
                dp[tx][ty][job]=1;
                q.push(vector<int>{cnt,tx,ty,job});
            }
        }
    }

    cout<<-1<<endl;

    return 0;
}