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

using ll = long long;
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define all(v) begin(v), end(v)

const int MAX_P = 100000;
int main() {
  int H, W;
  cin >> H >> W;
  array<int, 2> S, G;
  cin >> S[0] >> S[1];
  --S[0], --S[1];
  cin >> G[0] >> G[1];
  --G[0], --G[1];
  vector<string> C(H);
  for (auto &s : C) cin >> s;
  if (S[0] > G[0]) {
    S[0] = H - 1 - S[0];
    G[0] = H - 1 - G[0];
    reverse(all(C));
  }
  if (S[1] > G[1]) {
    S[1] = W - 1 - S[1];
    G[1] = W - 1 - G[1];
    for (auto &s : C) reverse(all(s));
  }
  vector dist(H, vector(W, vector(H * W, array<int,2>())));
  using ai4 = array<int, 4>;
  rep(i,H){
    rep(j,W){
      rep(k,H*W){
        rep(l,2)dist[i][j][k][l]=1e9;
      }
    }
  }
  dist[S[0]][S[1]][0][0] = 0;
  deque<ai4> bfs;
  bfs.push_back(ai4{S[0], S[1], 0, 0});
  auto move_ok = [&](int x, int y) -> bool {
    if (x < 0 || x >= H || y < 0 || y >= W) return false;
    return C[x][y] != '#';
  };
  while (!bfs.empty()) {
    auto [x, y, dA, f] = bfs.front();
    bfs.pop_front();
    int dC = dist[x][y][dA][f];
    if (dA + 1 < H * W) {
      // A
      int x2 = x - 1, y2 = y;
      if (move_ok(x2, y2) && dist[x2][y2][dA + 1][f] > dC) {
        dist[x2][y2][dA + 1][f] = dC;
        bfs.push_front(ai4{x2, y2, dA + 1, f});
      }
    }
    {
      // B
      int x2 = x + 1, y2 = y;
      if (move_ok(x2, y2) && dist[x2][y2][dA][f] > dC) {
        dist[x2][y2][dA][f] = dC;
        bfs.push_front(ai4{x2, y2, dA, f});
      }
    }
    {
      // C
      int x2 = x, y2 = y - 1;
      if (move_ok(x2, y2) && dist[x2][y2][dA][f | 1] > dC + 1) {
        dist[x2][y2][dA][f | 1] = dC + 1;
        bfs.push_back(ai4{x2, y2, dA, f | 1});
      }
    }
    {
      // D
      int x2 = x, y2 = y + 1;
      if (move_ok(x2, y2) && dist[x2][y2][dA][f] > dC) {
        dist[x2][y2][dA][f] = dC;
        bfs.push_front(ai4{x2, y2, dA, f});
      }
    }
  }
  vector prime(MAX_P, true);
  prime[0] = prime[1] = 0;
  for (ll i = 2; i < MAX_P; i++) {
    if (!prime[i]) continue;
    for (ll j = i * i; j < MAX_P; j += i) prime[j] = 0;
  }
  vector<int> pH, pW;
  rep(i, MAX_P - (G[0] - S[0])) {
    if (prime[i] && prime[i + (G[0] - S[0])]) pH.push_back(i);
  }
  rep(i, MAX_P - (G[1] - S[1])) {
    if (prime[i] && prime[i + (G[1] - S[1])]) pW.push_back(i);
  }
  int ans = 1e9;
  rep(i, H * W) {
    if (!i) continue;
    int c = dist[G[0]][G[1]][i][1];
    auto itH = lower_bound(all(pH), i);
    auto itW = lower_bound(all(pW), c);
    if (itH != end(pH) && itW != end(pW)) {
      ans = min(ans, (*itH) * 2 + (G[0] - S[0]) + (*itW) * 2 + (G[1] - S[1]));
    }
  }
  if (ans == 1e9)
    cout << "-1\n";
  else
    cout << ans << '\n';
}