#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <iostream>
#include <vector>
#include <string>
#include <sstream>
#include <algorithm>
#include <utility>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <functional>

using namespace std;

#define fst first
#define scd second
#define PB push_back
#define MP make_pair
#define int long long
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define omajinai ios::sync_with_stdio(false);cin.tie(0)

typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> pii;
typedef vector<pii> vpii;

template<typename T>T& max(T&a,T&b){if(a>=b)return a;return b;}
template<typename T>T& min(T&a,T&b){if(a<b)return a;return b;}
template<typename T>bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<typename T>bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}
template<typename T>T get(){T a;cin>>a;return a;}
template<typename T>T rev(T a){reverse(all(a));return a;}
template<typename T>vector<T>&sort(vector<T>&a){sort(all(a));return a;}

const int inf = 1e9;
const ll linf = 3e18;
const double eps = 1e-9;

struct data {
    int t, y, x;
    data(int t, int y, int x):t(t),y(y),x(x){}
};

char fld[502][502];

int dist[2][502][502];

int dx0[8] = {-2, -1, 1, 2, -2, -1, 1, 2}, dy0[8] = {-1, -2, -2, -1, 1, 2, 2, 1};
int dx1[4] = {-1, 1, -1, 1}, dy1[4] = {-1, -1, 1, 1};

int H, W;

bool inside(int y, int x)
{
    return (0 <= y && y < H && 0 <= x && x < W);
}

signed main()
{
    cin >> H >> W;

    for (int i = 0; i < 2; ++i) {
        for (int j = 0; j < H; ++j) {
            for (int k = 0; k < W; ++k) {
                dist[i][j][k] = inf;
            }
        }
    }

    int sx, sy, gy, gx;

    for (int i = 0; i < H; ++i) for (int j = 0; j < W; ++j) {
        cin >> fld[i][j];
        if (fld[i][j] == 'S') {
            sy = i, sx = j;
        } else if (fld[i][j] == 'G') {
            gy = i, gx = j;
        }
    }

    queue<data> q;
    q.push(data(0, sy, sx));
    dist[0][sy][sx] = 0;

    while (q.size()) {
        data d = q.front(); q.pop();

        if (d.t == 0) {
            for (int i = 0; i < 8; ++i) {
                int ny = d.y + dy0[i], nx = d.x + dx0[i];

                if (!inside(ny, nx)) continue;

                if (fld[ny][nx] == 'R') {
                    if (dist[0][d.y][d.x] + 1 < dist[1][ny][nx]) {
                        dist[1][ny][nx] = dist[0][d.y][d.x] + 1;
                        q.push(data(1, ny, nx));
                    }
                } else {
                    if (dist[0][d.y][d.x] + 1 < dist[0][ny][nx]) {
                        dist[0][ny][nx] = dist[0][d.y][d.x] + 1;
                        q.push(data(0, ny, nx));
                    }
                }
            }
        } else {
            for (int i = 0; i < 4; ++i) {
                int ny = d.y + dy1[i], nx = d.x + dx1[i];

                if (!inside(ny, nx)) continue;

                if (fld[ny][nx] == 'R') {
                    if (dist[1][d.y][d.x] + 1 < dist[0][ny][nx]) {
                        dist[0][ny][nx] = dist[1][d.y][d.x] + 1;
                        q.push(data(0, ny, nx));
                    }
                } else {
                    if (dist[1][d.y][d.x] + 1 < dist[1][ny][nx]) {
                        dist[1][ny][nx] = dist[1][d.y][d.x] + 1;
                        q.push(data(1, ny, nx));
                    }
                }
            }
        }
    }

    int mi = min(dist[0][gy][gx], dist[1][gy][gx]);

    cout << (mi == inf ? -1 : mi) << endl;
}