#include <bits/stdc++.h>
using namespace std;
using i64 = int64_t;
using vi = vector<i64>;
using vvi = vector<vi>;

int main() {
    int h, w;
    cin >> h >> w;
    vvi b(h, vi(w));
    int sx, sy, gx, gy;
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            char c;
            cin >> c;
            if (c == 'S') {
                sx = i, sy = j;
            } else if (c == 'G') {
                gx = i, gy = j;
            } else if (c == 'R') {
                b[i][j] = 1;
            }
        }
    }

    using ii = pair<int, int>;
    using iii = pair<ii, int>;
    vvi nowk(h, vi(w, 1e18)), nowb(h, vi(w, 1e18));
    queue<iii> que;
    que.push(iii(ii(sx, sy), 0));
    nowk[sx][sy] = 0;
    int dxk[] = {1, 2, 2, 1, -1, -2, -2, -1};
    int dyk[] = {2, 1, -1, -2, -2, -1, 1, 2};
    int dxb[] = {1, 1, -1, -1};
    int dyb[] = {-1, 1, -1, 1};
    auto ok = [&](int i, int j) {
        return 0 <= i && i < h && 0 <= j && j < w;
    };
    while (que.size()) {
        iii t = que.front();
        int x = t.first.first;
        int y = t.first.second;
        que.pop();
        if (t.second == 0) {
            for (int i = 0; i < 8; i++) {
                int xx = x + dxk[i];
                int yy = y + dyk[i];
                if (ok(xx, yy)) {
                    if (b[xx][yy]) {
                        if (t.second == 0) {
                            int p = nowk[x][y] + 1;
                            if (p < nowb[xx][yy]) {
                                nowb[xx][yy] = p;
                                que.push(iii(ii(xx, yy), 1));
                            }
                        } else {
                            int p = nowb[x][y] + 1;
                            if (p < nowk[xx][yy]) {
                                nowk[xx][yy] = p;
                                que.push(iii(ii(xx, yy), 0));
                            }
                        }
                    } else {
                        if (t.second == 0) {
                            int p = nowk[x][y] + 1;
                            if (p < nowk[xx][yy]) {
                                nowk[xx][yy] = p;
                                que.push(iii(ii(xx, yy), 0));
                            }
                        } else {
                            int p = nowb[x][y] + 1;
                            if (p < nowb[xx][yy]) {
                                nowb[xx][yy] = p;
                                que.push(iii(ii(xx, yy), 1));
                            }
                        }
                    }
                }
            }
        } else {
            for (int i = 0; i < 4; i++) {
                int xx = x + dxb[i];
                int yy = y + dyb[i];
                if (ok(xx, yy)) {
                    if (b[xx][yy]) {
                        if (t.second == 0) {
                            int p = nowk[x][y] + 1;
                            if (p < nowb[xx][yy]) {
                                nowb[xx][yy] = p;
                                que.push(iii(ii(xx, yy), 1));
                            }
                        } else {
                            int p = nowb[x][y] + 1;
                            if (p < nowk[xx][yy]) {
                                nowk[xx][yy] = p;
                                que.push(iii(ii(xx, yy), 0));
                            }
                        }
                    } else {
                        if (t.second == 0) {
                            int p = nowk[x][y] + 1;
                            if (p < nowk[xx][yy]) {
                                nowk[xx][yy] = p;
                                que.push(iii(ii(xx, yy), 0));
                            }
                        } else {
                            int p = nowb[x][y] + 1;
                            if (p < nowb[xx][yy]) {
                                nowb[xx][yy] = p;
                                que.push(iii(ii(xx, yy), 1));
                            }
                        }
                    }
                }
            }
        }
    }

    i64 k = min(nowk[gx][gy], nowb[gx][gy]);
    cout << (k == 1e18 ? -1 : k) << endl;
}