#include <iostream>
#include <algorithm>
#include <queue>
using namespace std;

const int inf = 987654321;
int gr, gc;
int R, C;
vector<string> G;
vector<vector<vector<bool>>> seen;
const vector<vector<int>> dr = {{2, 2, 1, 1, -1, -1, -2, -2}, {1, 1, -1, -1}},
                          dc = {{1, -1, 2, -2, 2, -2, 1, -1}, {1, -1, 1, -1}};

int nya(queue<tuple<int, int, bool, int>> que) {
  while(!que.empty()) {
    int r, c, cnt; bool is_bishop; tie(r, c, is_bishop, cnt) = que.front(); que.pop();
    if(seen[is_bishop][r][c]) { continue; }
    seen[is_bishop][r][c] = true;
    if(r == gr && c == gc) { return cnt; }
    for(int i=0, n=dr[is_bishop].size(); i<n; ++i) {
      int nr = r + dr[is_bishop][i],
          nc = c + dc[is_bishop][i];
      if(nr < 0 || R <= nr || nc < 0 || C <= nc) { continue; }
      que.emplace(nr, nc, is_bishop^G[nr][nc]=='R', cnt+1);
    }
  }
  return inf;
}

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> R >> C;
  G.assign(R, "");
  for(int r=0; r<R; ++r) { cin >> G[r]; }
  int sr, sc;
  for(int r=0; r<R; ++r) {
    for(int c=0; c<C; ++c) {
      if(G[r][c] == 'S') { sr = r; sc = c; }
      if(G[r][c] == 'G') { gr = r; gc = c; }
    }
  }
  seen.assign(2, vector<vector<bool>>(R, vector<bool>(C, false)));
  queue<tuple<int, int, bool, int>> que;
  que.emplace(sr, sc, false, 0);
  int res = nya(que);
  if(res == inf) { res = -1; }
  cout << res << '\n';
  return 0;
}