#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int h, w;
    cin >> h >> w;

    vector<string> s(h);
    for (int i = 0; i < h; i++) cin >> s[i];

    int hh = 2 * h - 1;
    int ww = 2 * w - 1;
    int W = ww + 2;
    int H = hh + 2;
    int SZ = W * H;

    int ss = -1, gg = -1;
    vector<int> d(SZ, -1);

    auto norm = [&](int idx) {
        if (idx < 0) idx += SZ;   // Python の負の添字を再現
        return idx;
    };

    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            int idx = 2 * i * W + 2 * j;
            if (s[i][j] == 'S') ss = idx;
            else if (s[i][j] == 'G') gg = idx;
            else if (s[i][j] == '#') d[idx] = -2;
        }
    }

    for (int i = hh; i <= hh + 1; i++) {
        for (int j = 0; j < W; j++) {
            d[i * W + j] = -2;
        }
    }
    for (int i = 0; i < H; i++) {
        for (int j = ww; j <= ww + 1; j++) {
            d[i * W + j] = -2;
        }
    }

    deque<int> q;
    q.push_back(ss);
    d[ss] = 0;

    vector<int> dij = {1, -1, W, -W};
    vector<int> dij2;
    for (int x : dij) dij2.push_back(2 * x);
    vector<int> di2 = {2 * W, -2 * W};
    vector<int> dj2 = {2, -2};

    while (!q.empty()) {
        int i = q.front();
        q.pop_front();

        int ii = i / W;
        int jj = i % W;

        for (int D : dij) {
            int j = norm(i + D);
            if (d[j] == -1) {
                d[j] = d[i] + 1;
                q.push_back(j);
            }
        }

        if (ii % 2 == 0 && jj % 2 == 0) {
            for (int D : dij2) {
                int j = norm(i + D);
                if (d[j] == -1) {
                    d[j] = d[i] + 1;
                    q.push_back(j);
                }
            }
        }

        if (ii % 2 == 0 && jj % 2 == 1) {
            for (int D : di2) {
                int j = norm(i + D);
                if (d[j] == -1) {
                    d[j] = d[i] + 1;
                    q.push_back(j);
                }
            }
        }

        if (ii % 2 == 1 && jj % 2 == 0) {
            for (int D : dj2) {
                int j = norm(i + D);
                if (d[j] == -1) {
                    d[j] = d[i] + 1;
                    q.push_back(j);
                }
            }
        }

        if (d[gg] != -1) {
            cout << d[gg] << '\n';
            return 0;
        }
    }

    return 0;
}