#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <limits.h>
#include <map>
#include <queue>
#include <set>
#include <string.h>
#include <vector>

using namespace std;
typedef long long ll;

const int DY[12] = {-2, -2, -1, -1, 1, 1, 2, 2, -1, -1, 1, 1};
const int DX[12] = {-1, 1, -2, 2, -2, 2, -1, 1, -1, 1, -1, 1};

const int KNIGHT = 0;
const int BISHOP = 1;

struct Node {
  int y;
  int x;
  int dist;
  int type;

  Node(int y = -1, int x = -1, int dist = -1, int type = -1) {
    this->y = y;
    this->x = x;
    this->dist = dist;
    this->type = type;
  }
};

int main() {
  int H, W;
  cin >> H >> W;
  vector<string> S;
  int sy, sx, gy, gx;

  for (int y = 0; y < H; ++y) {
    string row;
    cin >> row;

    S.push_back(row);

    for (int x = 0; x < W; ++x) {
      if (S[y][x] == 'S') {
        sy = y;
        sx = x;
      }
      if (S[y][x] == 'G') {
        gy = y;
        gx = x;
      }
    }
  }

  queue<Node> que;
  que.push(Node(sy, sx, 0, KNIGHT));
  int visited[H][W][2];
  memset(visited, -1, sizeof(visited));

  while (not que.empty()) {
    Node node = que.front();
    que.pop();

    if (visited[node.y][node.x][node.type] != -1) continue;
    visited[node.y][node.x][node.type] = node.dist;

    // fprintf(stderr, "(%d, %d, %d, %d)\n", node.y, node.x, node.dist, node.type);

    if (node.type == KNIGHT) {
      for (int direct = 0; direct < 8; ++direct) {
        int ny = node.y + DY[direct];
        int nx = node.x + DX[direct];
        if (ny < 0 || H <= ny || nx < 0 || W <= nx) continue;

        if (S[ny][nx] == 'R') {
          que.push(Node(ny, nx, node.dist + 1, BISHOP));
        } else {
          que.push(Node(ny, nx, node.dist + 1, KNIGHT));
        }
      }
    } else {
      for (int direct = 8; direct < 12; ++direct) {
        int ny = node.y + DY[direct];
        int nx = node.x + DX[direct];
        if (ny < 0 || H <= ny || nx < 0 || W <= nx) continue;

        if (S[ny][nx] == 'R') {
          que.push(Node(ny, nx, node.dist + 1, KNIGHT));
        } else {
          que.push(Node(ny, nx, node.dist + 1, BISHOP));
        }
      }
    }
  }

  if (visited[gy][gx][KNIGHT] == -1 && visited[gy][gx][BISHOP] == -1) {
    cout << -1 << endl;
  } else if (visited[gy][gx][KNIGHT] == -1) {
    cout << visited[gy][gx][BISHOP] << endl;
  } else if (visited[gy][gx][BISHOP] == -1) {
    cout << visited[gy][gx][KNIGHT] << endl;
  } else {
    cout << min(visited[gy][gx][KNIGHT], visited[gy][gx][BISHOP]) << endl;
  }

  return 0;
}