#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <set>
#include <map>
#include <queue>
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <cctype>
#include <cassert>
#include <limits>
#include <functional>
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
#if defined(_MSC_VER) || __cplusplus > 199711L
#define aut(r,v) auto r = (v)
#else
#define aut(r,v) __typeof(v) r = (v)
#endif
#define each(it,o) for(aut(it, (o).begin()); it != (o).end(); ++ it)
#define all(o) (o).begin(), (o).end()
#define pb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))
#define mset(m,v) memset(m,v,sizeof(m))
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
using namespace std;
typedef vector<int> vi; typedef pair<int, int> pii; typedef vector<pair<int, int> > vpii; typedef long long ll;
template<typename T, typename U> inline void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> inline void amax(T &x, U y) { if(x < y) x = y; }

int g_W;
int geth(int i, int j, int k) {
	return (i * g_W + j) * 2 + k;
}

int main() {
	const int dy[2][8] = {
		{ 2,2,1,1,-1,-1,-2,-2 },
		{ 1,1,-1,-1 }
	};
	const int dx[2][8] = {
		{ 1,-1,2,-2,2,-2,1,-1 },
		{ 1,-1,1,-1 }
	};
	int H; int W;
	while(~scanf("%d%d", &H, &W)) {
		g_W = W;
		vector<vector<char>> s(H, vector<char>(W + 1));
		rep(i, H) scanf("%s", s[i].data());
		pii spos;
		rep(i, H) rep(j, W) if(s[i][j] == 'S')
			spos = mp(i, j);
		vector<bool> vis(H * W * 2);
		vi q;
		q.push_back(geth(spos.first, spos.second, 0));
		vis[geth(spos.first, spos.second, 0)] = true;
		int ans = -1, curd = 0;
		for(int h = 0, td = q.size(); h != q.size(); ++ h) {
			if(h == td) {
				++ curd;
				td = q.size();
			}
			int t = q[h];
			int i = t / 2 / W, j = t / 2 % W, k = t % 2;
			if(s[i][j] == 'G') {
				ans = curd;
				break;
			}
			rep(d, k == 0 ? 8 : 4) {
				int yy = i + dy[k][d], xx = j + dx[k][d];
				if(yy < 0 || yy >= H || xx < 0 || xx >= W) continue;
				int nk = k ^ (s[yy][xx] == 'R' ? 1 : 0);
				int nh = geth(yy, xx, nk);
				if(!vis[nh]) {
					vis[nh] = true;
					q.push_back(nh);
				}
			}
		}
		printf("%d\n", ans);
	}
	return 0;
}