#include <bits/stdc++.h>

#define _overload(_1,_2,_3,name,...) name
#define _rep(i,n) _range(i,0,n)
#define _range(i,a,b) for(int i=int(a);i<int(b);++i)
#define rep(...) _overload(__VA_ARGS__,_range,_rep,)(__VA_ARGS__)

#define _rrep(i,n) _rrange(i,n,0)
#define _rrange(i,a,b) for(int i=int(a)-1;i>=int(b);--i)
#define rrep(...) _overload(__VA_ARGS__,_rrange,_rrep,)(__VA_ARGS__)

#define _all(arg) begin(arg),end(arg)
#define uniq(arg) sort(_all(arg)),(arg).erase(unique(_all(arg)),end(arg))
#define getidx(ary,key) lower_bound(_all(ary),key)-begin(ary)
#define clr(a,b) memset((a),(b),sizeof(a))
#define bit(n) (1LL<<(n))
#define popcount(n) (__builtin_popcountll(n))

template<class T>bool chmax(T &a, const T &b) { return (a<b)?(a=b,1):0;}
template<class T>bool chmin(T &a, const T &b) { return (b<a)?(a=b,1):0;}

using namespace std;


string board[510];
int dist[510][510][2];

using state=tuple<int,int,int>;

int main(void){
	int h,w;
	cin >> h >> w;
	rep(i,h) cin >> board[i];

	clr(dist,-1);

	int sh,sw,gh,gw;
	rep(i,h)rep(j,w){
		if(board[i][j]=='S') sh=i,sw=j;
		if(board[i][j]=='G') gh=i,gw=j;
	}

	dist[sh][sw][0]=0;
	queue<state> q;
	q.push(state(sh,sw,0));

	while(!q.empty()){
		int ch,cw,type;
		tie(ch,cw,type)=q.front();q.pop();
		if(type==0){
			const int dh[8]={-2,-2,-1,-1,1,1,2,2};
			const int dw[8]={-1,1,-2,2,-2,2,-1,1};
			rep(i,8){
				int nh=ch+dh[i],nw=cw+dw[i],ntype=type;
				if(nh<0||h<=nh) continue;
				if(nw<0||w<=nw) continue;
				if(board[nh][nw]=='R') ntype^=1;
				if(dist[nh][nw][ntype]==-1){
					dist[nh][nw][ntype]=dist[ch][cw][type]+1;
					q.push(state(nh,nw,ntype));
				}
			}
		}else{
			const int dh[4]={-1,-1,1,1};
			const int dw[4]={-1,1,-1,1};
			rep(i,4){
				int nh=ch+dh[i],nw=cw+dw[i],ntype=type;
				if(nh<0||h<=nh) continue;
				if(nw<0||w<=nw) continue;
				if(board[nh][nw]=='R') ntype^=1;
				if(dist[nh][nw][ntype]==-1){
					dist[nh][nw][ntype]=dist[ch][cw][type]+1;
					q.push(state(nh,nw,ntype));
				}
			}
		}
	}

	int ans=1<<20;
	rep(i,2) if(dist[gh][gw][i]!=-1) chmin(ans,dist[gh][gw][i]);
	if(ans==(1<<20)) ans=-1;
	cout << ans << endl;
	return 0;
}