#include <iostream>
#include <vector>
#include <queue>
#include <list>
#include <map>
#include <string>
#include <cstdio>
#include<functional>

using namespace std;

int mapf[501][501];
int dp[501][501][2];

int w,h;

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

int main(){
    int i,j,k,l,m,n;
    int x,y;
    char ch;
    
    int sx,sy,gx,gy;
    
    cin >> h>>w;
    
    for (y=0;y<h;y++){
        for (x=0;x<w;x++){
            while ((cin >> ch),(ch!='S'&&ch!='G'&&ch!='R'&&ch!='.'));
            if (ch=='S'){
                sx=x;sy=y;
            }
            if (ch=='G'){
                gx=x;gy=y;
            }
            mapf[x][y]=ch;
        }
    }
    
    priority_queue<vector<int>,vector<vector<int>>, function<bool(vector<int>&,vector<int>&)>> qu([](vector<int> &vl,vector<int> &vr){return vl[4]>vr[4];});
    qu.push(vector<int>{sx,sy,0,0,0});
    
    while (!qu.empty()){
        vector<int> e=qu.top();
        qu.pop();
        x=e[0];y=e[1];
        
        if (mapf[x][y]=='R') e[2]=!e[2];
        if (mapf[x][y]=='G'){
            cout << e[3] << endl;
            return 0;
        }
        dp[x][y][e[2]]=1;
        k=abs(x-gx)+abs(y-gy);
        e[3]++;
        if (!e[2]){
            if (inbox(x-2,y-1)&& !dp[x-2][y-1][0]) qu.push(vector<int>{x-2,y-1,e[2],e[3],-k});
            if (inbox(x-2,y+1)&& !dp[x-2][y+1][0]) qu.push(vector<int>{x-2,y+1,e[2],e[3],-k});
            if (inbox(x-1,y-2)&& !dp[x-1][y-2][0]) qu.push(vector<int>{x-1,y-2,e[2],e[3],-k});
            if (inbox(x-1,y+2)&& !dp[x-1][y+2][0]) qu.push(vector<int>{x-1,y+2,e[2],e[3],-k});
            if (inbox(x+2,y-1)&& !dp[x+2][y-1][0]) qu.push(vector<int>{x+2,y-1,e[2],e[3],-k});
            if (inbox(x+2,y+1)&& !dp[x+2][y+1][0]) qu.push(vector<int>{x+2,y+1,e[2],e[3],-k});
            if (inbox(x+1,y-2)&& !dp[x+1][y-2][0]) qu.push(vector<int>{x+1,y-2,e[2],e[3],-k});
            if (inbox(x+1,y+2)&& !dp[x+1][y+2][0]) qu.push(vector<int>{x+1,y+2,e[2],e[3],-k});
        }else{
            if (inbox(x-1,y-1)&& !dp[x-1][y-1][1]) qu.push(vector<int>{x-1,y-1,e[2],e[3],-k});
            if (inbox(x-1,y+1)&& !dp[x-1][y+1][1]) qu.push(vector<int>{x-1,y+1,e[2],e[3],-k});
            if (inbox(x+1,y-1)&& !dp[x+1][y-1][1]) qu.push(vector<int>{x+1,y-1,e[2],e[3],-k});
            if (inbox(x+1,y+1)&& !dp[x+1][y+1][1]) qu.push(vector<int>{x+1,y+1,e[2],e[3],-k});
        }
    }
            
    cout << -1 << endl;
    return 0;
}