#include <bits/stdc++.h>

using namespace std;

// k: knight
const vector<int> kdx {-1, 1, -2, 2, -2, 2, -1, 1};
const vector<int> kdy {-2, -2, -1, -1, 1, 1, 2, 2};

// b: bishop
const vector<int> bdx {-1, 1, -1, 1};
const vector<int> bdy {-1, -1, 1, 1};

int H, W;
int sx, sy, gx, gy;
char board[500][500];
// k: minStep[][][0]
// b: minStep[][][1]
bool visited[500][500][2];

// k: piece == 0
// b: piece == 1
struct State {
    int x, y, step, piece;
    State() {}
    State(int _x, int _y, int _step, int _piece) :
        x(_x), y(_y), step(_step), piece(_piece) {}
};

int solve() {
    memset(visited, false, sizeof(visited));

    queue<State> Q;
    Q.push(State(sx, sy, 0, 0));
    visited[sy][sx][0] = true;

    while (!Q.empty()) {
        State stt = Q.front();
        Q.pop();

        vector<int> dx, dy;
        if (stt.piece == 0) {
            dx = kdx;
            dy = kdy;
        } else {
            dx = bdx;
            dy = bdy;
        }

        for (int i = 0; i < dx.size(); i++) {
            int x = stt.x + dx[i];
            int y = stt.y + dy[i];
            int piece = stt.piece;

            if (!(0 <= x && x < W) || !(0 <= y && y < H)) {
                continue;
            }

            if (x == gx && y == gy) {
                return stt.step + 1;
            }

            if (board[y][x] == 'R') {
                piece = 1 - piece;
            }

            if (visited[y][x][piece]) {
                continue;
            }

            visited[y][x][piece] = true;
            Q.push(State(x, y, stt.step + 1, piece));
        }
    }

    return -1;
}

int main() {
    cin >> H >> W;
    for (int i = 0; i < H; i++) {
        for (int j = 0; j < W; j++) {
            cin >> board[i][j];
            if (board[i][j] == 'S') {
                sy = i;
                sx = j;
            }
            if (board[i][j] == 'G') {
                gy = i;
                gx = j;
            }
        }
    }
    cout << solve() << endl;
    return 0;
}