#include <iostream>
#include <cstdio>
#include <vector>
#include <string>
#include <tuple>
#include <queue>
using namespace std;
int dp[2][500][500];
const int inf=1e9;
int nx[]={-2,-2,-1,-1,1,1,2,2};
int ny[]={1,-1,2,-2,2,-2,1,-1};
int bx[]={-1,-1,1,1};
int by[]={1,-1,1,-1};
int h,w;
bool isInField(int x,int y){
    if(x<0 or w<=x) return false;
    if(y<0 or h<=y) return false;
    return true;
}
int main(){
    cin>>h>>w;
    vector<string> s(h);
    int sx=0,sy=0;
    int gx=0,gy=0;
    for(int i=0;i<h;i++){
        cin>>s[i];
        for(int j=0;j<w;j++){
            if(s[i][j]=='S'){
                sx=j;   sy=i;
            }
            else if(s[i][j]=='G'){
                gx=j;   gy=i;
            }
        }
    }
    for(int i=0;i<h;i++){
        for(int j=0;j<w;j++)    dp[0][i][j]=dp[1][i][j]=inf;
    }
    queue<tuple<int,int,int> > q;
    dp[0][sy][sx]=0;
    q.push(make_tuple(0,sx,sy));
    while(!q.empty()){
        auto it=q.front();  q.pop();
        int mode=get<0>(it);
        int x=get<1>(it);
        int y=get<2>(it);
        if(x==gx and y==gy){
            cout<<dp[mode][y][x]<<endl;
            return 0;
        }
        if(mode==0){
            for(int i=0;i<8;i++){
                int dx=x+nx[i];
                int dy=y+ny[i];
                int nextmode=mode;
                if(!isInField(dx,dy))   continue;
                if(s[dy][dx]=='R'){
                    nextmode^=1;
                }
                if(dp[nextmode][dy][dx]>dp[mode][y][x]+1){
                    dp[nextmode][dy][dx]=dp[mode][y][x]+1;
                    q.push(make_tuple(nextmode,dx,dy));
                }
            }
        }
        else{
            for(int i=0;i<4;i++){
                int dx=x+bx[i];
                int dy=y+by[i];
                int nextmode=mode;
                if(!isInField(dx,dy))   continue;
                if(s[dy][dx]=='R'){
                    nextmode^=1;
                }
                if(dp[nextmode][dy][dx]>dp[mode][y][x]+1){
                    dp[nextmode][dy][dx]=dp[mode][y][x]+1;
                    q.push(make_tuple(nextmode,dx,dy));
                }
            }
        }
    }
    cout<<-1<<endl;
    return 0;
}