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

typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> veci;
typedef vector<string> vecs;
template<class T,class U> using Hash=unordered_map<T,U>;

#define REP(i, a, n) for(ll i = a; i < n; i++)
#define RREP(i, a, n) for(ll i = n-1; i >= a; i--)
#define rep(i, n) REP(i, 0, n)
#define rrep(i, n) RREP(i, 0, n)
#define MD 1000000007

template<class T> T read(){T a;cin >> a;return a;}
template<class T> void read(T& a){cin >> a;}
template<class T> void rarr(T a, int n){for(int i = 0; i < n; i++) {cin >> a[i];}}
template<class T> void write(T a){cout << a << endl;}
template<class T> void writes(vector<T> a, char* c = " "){cout << a[0];for(int i = 1; i < a.size(); i++)cout << c << a[i];cout << endl;;}
void write(double a){cout << fixed << setprecision(12) << a << endl;}
template<class T> void warr(T a, int n, char* c = " "){cout << a[0];for(int i = 1; i < n; i++)cout << c << a[i];cout << endl;}
void split(string s, string delim, veci& result){result.clear();string::size_type pos = 0;while(pos != string::npos){string::size_type p = s.find(delim, pos);if(p == string::npos){result.push_back(atoi(s.substr(pos).data()));break;}else {result.push_back(atoi(s.substr(pos, p - pos).data()));}pos = p + delim.size();}}
void split(string s, string delim, vecs& result){result.clear();string::size_type pos = 0;while(pos != string::npos){string::size_type p = s.find(delim, pos);if(p == string::npos){result.push_back(s.substr(pos));break;}else {result.push_back(s.substr(pos, p - pos));}pos = p + delim.size();}}
ll gcd(ll a, ll b){while(true){ll k = a % b;if(k == 0)return b;a = b;b = k;}}
ll comb(ll n, ll m){ll p=1;m=min(m,n-m);for(ll i=1;i<=m;i++){p*=n-i+1;p/=i;}return p;}

int dax[]={1,2,-1,-2,1,2,-1,-2};
int day[]={2,1,-2,-1,-2,-1,2,1};
int dbx[]={1,-1,-1,1};
int dby[]={1,1,-1,-1};
int w,h;
bool b[500][500]={0};
int gx,gy;
const int MAX=10000000;

typedef pair<int,pair<int, int>> s_pair;
s_pair mp(bool a, int b, int c){
    s_pair p;
    p.first=a;
    p.second.first=b;
    p.second.second=c;
    return p;
}

int main(void)
{
    int sx,sy;
    int a[500][500][2]={0};
    cin>>h>>w;
    rep(i,h){
        string s;
        cin>>s;
        rep(j,w){
            b[i][j]=(s[j]=='R');
            a[i][j][0]=a[i][j][1]=MAX;
            if(s[j]=='S'){
                sy=i;sx=j;
            }
            else if(s[j]=='G'){
                gy=i;gx=j;
            }
        }
    }
    queue<s_pair> q;
    q.push(mp(false,sx,sy));
    a[sy][sx][0]=0;
    while(!q.empty()){
        s_pair p=q.front();
        q.pop();
        bool bp=p.first;
        int x=p.second.first;
        int y=p.second.second;
        int bb=(b[y][x])?!bp:bp;
        int *dx=(!bp)?dax:dbx;
        int *dy=(!bp)?day:dby;
        int lim=(!bp)?8:4;
        rep(i,lim){
            int cx=x+dx[i];
            int cy=y+dy[i];
            if(cx>=w||cx<0||cy>=h||cy<0)continue;
            if(a[cy][cx][(int)bp]!=MAX)continue;
            a[cy][cx][bp]=a[y][x][bb]+1;
            if(b[cy][cx])
                q.push(mp(!bp,cx,cy));
            else
                q.push(mp(bp,cx,cy));
        }
    }
    /*
    rep(i,h){
        rep(j,w)
            cout<<min(a[i][j][0],a[i][j][1]);
        cout<<endl;
    }
    */
    int res=min(a[gy][gx][0],a[gy][gx][1]);
    if(res!=MAX)
        write(res);
    else write(-1);
    return 0;
}