#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>
#include <functional>
#include <set>
#include <ctime>
#include <random>
#include <chrono>
#include <cassert>
using namespace std;

namespace {
	using Integer = long long; //__int128;
	template<class T> istream& operator >> (istream& is, vector<T>& vec){for(T& val: vec) is >> val; return is;}
	template<class T> istream& operator ,  (istream& is, T& val){ return is >> val;}
	template<class T> ostream& operator << (ostream& os, const vector<T>& vec){for(int i=0; i<vec.size(); i++) os << vec[i] << (i==vec.size()-1?"":" "); return os;}
	template<class T> ostream& operator ,  (ostream& os, const T& val){ return os << " " << val;}

	template<class H> void print(const H& head){ cout << head; }
	template<class H, class ... T> void print(const H& head, const T& ... tail){ cout << head << " "; print(tail...); }
	template<class ... T> void println(const T& ... values){ print(values...); cout << endl; }

	template<class H> void eprint(const H& head){ cerr << head; }
	template<class H, class ... T> void eprint(const H& head, const T& ... tail){ cerr << head << " "; eprint(tail...); }
	template<class ... T> void eprintln(const T& ... values){ eprint(values...); cerr << endl; }

	string operator "" _s (const char* str, size_t size){ return move(string(str)); }
	constexpr Integer my_pow(Integer x, Integer k, Integer z=1){return k==0 ? z : k==1 ? z*x : (k&1) ? my_pow(x*x,k>>1,z*x) : my_pow(x*x,k>>1,z);}
	constexpr Integer my_pow_mod(Integer x, Integer k, Integer M, Integer z=1){return k==0 ? z%M : k==1 ? z*x%M : (k&1) ? my_pow_mod(x*x%M,k>>1,M,z*x%M) : my_pow_mod(x*x%M,k>>1,M,z);}
	constexpr unsigned long long operator "" _ten (unsigned long long value){ return my_pow(10,value); }

	inline int k_bit(Integer x, int k){return (x>>k)&1;} //0-indexed

	mt19937 mt(chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count());

	template<class T> string join(const vector<T>& v, const string& sep){
		stringstream ss; for(int i=0; i<v.size(); i++){ if(i>0) ss << sep; ss << v[i]; } return ss.str();
	}
}

constexpr long long mod = 9_ten + 7;

int main(){
	int h,w;
	cin >> h,w;
	vector<string> v(h);
	cin >> v;

	int s,t;
	for(int i=0; i<h; i++) for(int j=0; j<w; j++){
		if(v[i][j] == 'G') t = i*w + j;
		if(v[i][j] == 'S') s = i*w + j;
	}

	vector<long long> dist(2*h*w, 1145148931919LL);
	dist[s<<1] = 0;

	queue<int> q;
	q.push( s<<1 );

	int dx[] = {+1,+1,-1,-1,+2,+2,-2,-2, +1,+1,-1,-1};
	int dy[] = {+2,-2,+2,-2,+1,-1,+1,-1, +1,-1,+1,-1};
	
	while(q.size()){
		auto p = q.front();
		q.pop();
		
		for(int k= ((p&1)?8:0); k<((p&1)?12:8); k++){
			int xx = (p>>1)%w + dx[k];
			int yy = (p>>1)/w + dy[k];
			if(xx<0 || xx>=w || yy<0 || yy>=h) continue;
			int next = (xx + yy*w) << 1;
			next |= p&1;
			if(v[yy][xx] == 'R') next ^= 1;
			if(dist[next] >= 1145148931919LL){
				dist[next] = dist[p] + 1;
				q.push(next);
			}
		}
	}

	long long ans = min(dist[t<<1], dist[(t<<1)|1]);
	println( ans == 1145148931919LL ? -1 : ans);
	return 0;
}