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

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int h, w, sy, sx, gy, gx;
    cin >> h >> w;
    vector<string> A(h);
    for(int y = 0; y < h; y++){
        cin >> A[y];
        for(int x = 0; x < w; x++){
            if(A[y][x] == 'S') sy = y, sx = x;
            if(A[y][x] == 'G') gy = y, gx = x;
        }
    }
    vector<vector<pair<int,int>>> dir = {
        {{-1, -2}, {-1, 2}, {1, -2}, {1, 2}, {2, 1}, {2, -1}, {-2, -1}, {-2, 1}},
        {{1, 1}, {1, -1}, {-1, 1}, {-1, -1}}
    };
    queue<tuple<int,int,int>> nxt;
    vector<vector<array<int,2>>> dp(h, vector<array<int,2>>(w, array<int,2>({1 << 30, 1 << 30})));
    dp[sy][sx][0] = 0;
    nxt.emplace(sy, sx, 0);
    while(!nxt.empty()){
        int y, x, s, dy, dx, ny, nx, ns;
        tie(y, x, s) = nxt.front();
        nxt.pop();
        for(auto &&p : dir[s]){
            tie(dy, dx) = p;
            ny = y + dy;
            nx = x + dx;
            if(ny < 0 || ny >= h || nx < 0 || nx >= w) continue;
            ns = s ^ (A[ny][nx] == 'R');
            if(dp[y][x][s] + 1 >= dp[ny][nx][ns]) continue;
            dp[ny][nx][ns] = dp[y][x][s] + 1;
            nxt.emplace(ny, nx, ns);
        }
    }
    int ans = min(dp[gy][gx][0], dp[gy][gx][1]);
    if(ans == (1 << 30)) ans = -1;
    cout << ans << '\n';
}