#ifdef __GNUC__
#pragma GCC optimize ("O3")
#pragma GCC target ("avx")
#endif

#define _USE_MATH_DEFINES

#include <iostream>
#include <iomanip>
#include <stdio.h>

#include <sstream>
#include <algorithm>
#include <cmath>

#include <string>
#include <cstring>
#include <vector>
#include <valarray>
#include <array>

#include <queue>
#include <complex>
#include <set>
#include <map>
#include <stack>
#include <list>

#include <cassert>//assert();
#include <fstream>
/////////
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)

/////////
typedef long long LL;
typedef long double LD;
typedef unsigned long long ULL;
#define PII pair<int,int>
/////////
using namespace::std;

// 最大公約数
template<class T>
inline T gcd(T a, T b){return b == 0 ? a : gcd(b, a % b);}
// 最小公倍数
template<class T>
inline T lcm(T a, T b){return a * b / gcd(a, b);}
////////////////////////////////
struct data{
	int x;
	int y;
	int turn;
	int kind;//0 kNi, 1 bisyo
};
inline void solve(){
	int H,W;
	cin >> H>>W;
	vector<string> ban(H);
	vector<vector< vector<bool> >> sta(2,vector<vector<bool>>(H,vector<bool>(W,false)));
	data start,goal,temp,next;
	queue< data > que;

	for(int i=0;i<H;++i){
		cin >> ban[i];
		for(int j=0;j<W;++j){
			if( ban[i][j] == 'S' ){
				start.x = j;
				start.y = i;
			}else if( ban[i][j] == 'G' ){
				goal.x = j;
				goal.y = i;
			}
		}
	}
	start.turn = 0;
	start.kind = 0;
	if( start.x == goal.x && start.y == goal.y ){
		printf("-\n");
		return;
	}
	que.push( start );
	sta[0][start.y][start.x] = true;
	int sizeB = 4;
	int dxB[] = { 1, 1,-1,-1};
	int dyB[] = { 1,-1, 1,-1};
	int sizeK = 8;
	int dxK[] = { 2, 2, 1, 1,-1,-1,-2,-2};
	int dyK[] = { 1,-1, 2,-2,+2,-2,+1,-1};
	while( !que.empty() ){
		temp = que.front();
		que.pop();
		if( temp.kind == 1){
			//ミニビショップ
			for(int i=0;i<sizeB;++i){
				next.x = temp.x + dxB[i];
				next.y = temp.y + dyB[i];
				if( 0 <= next.x && next.x < W &&
					0 <= next.y && next.y < H){
						next.kind = temp.kind;
						if( ban[next.y][next.x] == 'R' ){
							next.kind = (next.kind+1)%2;
						}
						if( sta[next.kind][next.y][next.x] == false ){
							next.turn = temp.turn + 1;
							if( next.x == goal.x && next.y == goal.y){
								printf("%d\n",next.turn);
								return;
							}
							sta[next.kind][next.y][next.x] = true;
							que.push( next );
						}
				}
			}
		}else{
			//ナイト
			for(int i=0;i<sizeK;++i){
				next.x = temp.x + dxK[i];
				next.y = temp.y + dyK[i];
				if( 0 <= next.x && next.x < W &&
					0 <= next.y && next.y < H){
						next.kind = temp.kind;
						if( ban[next.y][next.x] == 'R' ){
							next.kind = (next.kind+1)%2;
						}
						if( sta[next.kind][next.y][next.x] == false ){
							next.turn = temp.turn + 1;
							if( next.x == goal.x && next.y == goal.y){
								printf("%d\n",next.turn);
								return;
							}
							sta[next.kind][next.y][next.x] = true;
							que.push( next );
						}
				}
			}
		}
	}
	printf("-1\n");
}

int main(void){
    std::cin.tie(0);
    std::ios::sync_with_stdio(false);
	//std::cout << std::fixed;//小数を10進数表示
    //cout << setprecision(16);//小数をいっぱい表示する。16?

	solve();

	return 0;
}