Problem p02579 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> Pii;
typedef pair<int, ll> Pil;
typedef pair<ll, ll> Pll;
typedef pair<int, ld> Pid;
typedef pair<int, string> Pis;
#define rep(i, n) for (int i = 0; i < n; i++)
#define repm(i, s, n) for (int i = s; i < n; i++)
#define all(a) (a).begin(), (a).end()

const int INF = 1 << 30;
const ll INF_L = 1LL << 60;
const int MOD = 1e9 + 7; // 998244353;

void coi(ll i) { cout << i << endl; }
void cois(ll i) { cout << i << " "; }
void cod(ld d) {
  cout << fixed << setprecision(16);
  cout << d << endl;
}
void cods(ld d) {
  cout << fixed << setprecision(16);
  cout << d << " ";
}
void coc(char c) { cout << c << endl; }
void cocs(char c) { cout << c << " "; }
void cos(string s) { cout << s << endl; }
void coss(string s) { cout << s << " "; }
void coynl(bool b) { cos(b ? "Yes" : "No"); }
void coYNU(bool b) { cos(b ? "YES" : "NO"); }

// ----------------------------------------------------------------
// String Functions
// ----------------------------------------------------------------
int ctoi(char c) {
  if (isdigit(c))
    return c - '0';
  else if (islower(c))
    return c - 'a';
  else if (isupper(c))
    return c - 'A';
  else
    return -1;
}
char itocd(int i) {
  char c = i + '0';
  if (isdigit(c))
    return c;
  else
    return 0x00;
}
char itocl(int i) {
  char c = i + 'a';
  if (islower(c))
    return c;
  else
    return 0x00;
}
char itocu(int i) {
  char c = i + 'A';
  if (isupper(c))
    return c;
  else
    return 0x00;
}
// ----------------------------------------------------------------

// ----------------------------------------------------------------
// Dynamical Programming
// ----------------------------------------------------------------
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
// ----------------------------------------------------------------

// ----------------------------------------------------------------
// Graph Theory
// ----------------------------------------------------------------
struct edge {
  ll to, cost;
};
struct graph_list {
  ll V;
  vector<vector<edge>> graph;
  vector<ll> dist;

  graph_list(ll n) { init(n); }
  void init(ll n) {
    V = n;
    graph.resize(V);
    dist.resize(V);
    for (int i = 0; i < V; i++) {
      dist[i] = INF_L;
    }
  }
  void add_edge(ll from, ll to, ll cost) {
    edge e;
    e.to = to;
    e.cost = cost;
    graph[from].push_back(e);
  }

  void dijkstra(ll s) {
    for (int i = 0; i < V; i++) {
      dist[i] = INF_L;
    }
    dist[s] = 0;

    priority_queue<Pll, vector<Pll>, greater<Pll>> que;
    que.push(Pll(0, s));
    while (!que.empty()) {
      Pll p = que.top();
      que.pop();
      ll v = p.second;
      if (dist[v] < p.first)
        continue;
      for (auto e : graph[v]) {
        if (dist[e.to] > dist[v] + e.cost) {
          dist[e.to] = dist[v] + e.cost;
          que.push(Pll(dist[e.to], e.to));
        }
      }
    }
  }
  void bellman_ford(ll s) {
    for (int i = 0; i < V; i++) {
      dist[i] = INF_L;
    }
    dist[s] = 0;
  }
};
struct graph_matrix {
  ll vertex;
  vector<vector<edge>> graph;
  vector<ll> dist;

  graph_matrix(ll n) { init(n); }
  void init(ll n) {
    vertex = n;
    graph.resize(vertex);
    dist.resize(vertex);
    for (int i = 0; i < vertex; i++) {
      dist[i] = INF;
    }
  }
  void add_edge(ll s, ll t, ll cost) {
    edge e;
    e.to = t;
    e.cost = cost;
    graph[s].push_back(e);
  }

  void warshall_floyd(ll s) {
    for (int i = 0; i < vertex; i++) {
      dist[i] = INF;
    }
    dist[s] = 0;
  }
};
// ----------------------------------------------------------------

// ----------------------------------------------------------------
// Mathematical Functions
// ----------------------------------------------------------------
ll gcd(ll A, ll B) {
  if (A % B == 0) {
    return (B);
  } else {
    return (gcd(B, A % B));
  }
}
ll lcm(ll A, ll B) { return A * B / gcd(A, B); }

ll getDigit(ll N) { return (ll)(to_string(N).length()); }
ll getDigitForBase(ll N, ll B) {
  if (B < 2) {
    return -1;
  } else if (B == 10) {
    return getDigit(N);
  } else {
    ll r = 0;
    while (N != 0) {
      N /= B;
      r++;
    }
    return r;
  }
}
ll getDivTimes(ll N, ll D) {
  ll r = 0;
  while (N % D == 0) {
    N /= D;
    r++;
  }
  return r;
}

ll powMod(ll B, ll P) {
  if (P == 0)
    return 1;
  if (P % 2 == 0) {
    ll t = powMod(B, P / 2);
    return t * t % MOD;
  }
  return B * powMod(B, P - 1) % MOD;
}

/* ----------------------------------
 Factorial, Permutation, Combination
 ---------------------------------- */
const int FAC_INIT_SIZE = 1e6 + 9;
vector<ll> fac, finv, inv;

void factModInit() {
  fac.resize(FAC_INIT_SIZE);
  finv.resize(FAC_INIT_SIZE);
  inv.resize(FAC_INIT_SIZE);
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < FAC_INIT_SIZE; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}
ll factMod(ll N) { return fac[N] % MOD; }
ll factInvMod(ll N) { return finv[N] % MOD; }
ll permMod(ll N, ll K) {
  if (N < 0 || K < 0 || N < K)
    return 0;
  else
    return factMod(N) * factInvMod(N - K) % MOD;
}
ll combMod(ll N, ll K) {
  if (N < 0 || K < 0 || N < K)
    return 0;
  else if (N < FAC_INIT_SIZE) {
    return factMod(N) * (factInvMod(K) * factInvMod(N - K) % MOD) % MOD;
  } else {
    ll ans = 1;
    ll Ks = K < N - K ? K : N - K;
    for (ll i = N; i > N - Ks; i--) {
      ans *= i;
      ans %= MOD;
    }
    return ans * factInvMod(Ks) % MOD;
  }
}

/* ----------------------------------
 Sieve of Atkin & Bernstein
 ---------------------------------- */
vector<bool> sieve;
void sieveInit(ll size) {
  sieve.clear();
  if (size < 0 || size > INF)
    return;

  int ss = (int)size + 9;
  int ssq = sqrt(ss + 0.1);
  sieve.resize(ss);
  sieve[2] = sieve[3] = true;

  int n = 0;
  for (int z = 1; z <= 5; z += 4) {
    for (int y = z; y <= ssq; y += 6) {
      for (int x = 1; x <= ssq && (n = 4 * x * x + y * y) < ss; x++)
        sieve[n] = !sieve[n];
      for (int x = y + 1; x <= ssq && (n = 3 * x * x - y * y) < ss; x += 2)
        sieve[n] = !sieve[n];
    }
  }
  for (int z = 2; z <= 4; z += 2) {
    for (int y = z; y <= ssq; y += 6) {
      for (int x = 1; x <= ssq && (n = 3 * x * x + y * y) < ss; x += 2)
        sieve[n] = !sieve[n];
      for (int x = y + 1; x <= ssq && (n = 3 * x * x - y * y) < ss; x += 2)
        sieve[n] = !sieve[n];
    }
  }
  for (int z = 1; z <= 2; z++) {
    for (int y = 3; y <= ssq; y += 6) {
      for (int x = z; x <= ssq && (n = 4 * x * x + y * y) < ss; x += 3)
        sieve[n] = !sieve[n];
    }
  }
  for (int k = 5; k <= ssq; k++)
    if (sieve[k])
      for (int n = k * k; n < ss; n += k * k)
        sieve[n] = false;
}

/* ----------------------------------
 Prime Factorization
---------------------------------- */
map<ll, map<ll, ll>> primeFactorMap;
map<ll, set<ll>> primeFactorSet;
void primeFactorizeInit() {
  primeFactorMap.clear();
  primeFactorSet.clear();
}
void primeFactorize(ll N) {
  if (N < 0 || N > INF_L)
    return;

  ll Nc = N, Nsq = sqrt(N + 0.1);
  for (int k = 2; k <= Nsq; k++) {
    ll dt = 0;
    while (Nc % k == 0) {
      dt++;
      Nc /= k;
    }
    if (dt > 0)
      primeFactorMap[N][k] = dt;
    if (N % k == 0) {
      primeFactorSet[N].insert(k);
      primeFactorSet[N].insert(N / k);
    }
  }
  if (Nc != 1)
    primeFactorMap[N][Nc] = 1;
  primeFactorSet[N].insert(1);
  primeFactorSet[N].insert(N);
}
// ----------------------------------------------------------------

//* ****************  GLOBAL VARIABLES  **************** *//
int H, W;
int Ch, Cw;
int Dh, Dw;
vector<string> S;
//* **************************************************** *//

void input() {
  cin >> H >> W;
  cin >> Ch >> Cw;
  Ch--;
  Cw--;
  cin >> Dh >> Dw;
  Dh--;
  Dw--;
  S.resize(H);
  rep(i, H) cin >> S[i];
}

void solve() {

  graph_list g(H * W);
  rep(h, H) {
    rep(w, W) {
      if (S[h][w] == '#')
        continue;
      int ghw = h * H + w;
      if (h != 0)
        g.add_edge(ghw, ghw, 0);
      repm(dh, -2, 3) {
        repm(dw, -2, 3) {
          int nh = h + dh, nw = w + dw;
          int gdhw = nh * H + nw;
          if (nh < 0 || nh >= H || nw < 0 || nw >= W)
            continue;
          if (S[nh][nw] == '#')
            continue;
          if (abs(dh) + abs(dw) == 0)
            continue;
          //                    if(abs(dh) + abs(dw) == 1) g.add_edge(ghw, gdhw,
          //                    0); if(abs(dh) + abs(dw) > 1) g.add_edge(ghw,
          //                    gdhw, 1);
        }
      }
    }
  }
  // g.dijkstra(Ch * H + Cw);
  // coi(g.dist[Dh * H + Dw] == INF_L ? -1 : g.dist[Dh * H + Dw]);

  vector<vector<int>> SD(H, vector<int>(W, INF));
  SD[Ch][Cw] = 0;

  int dh[4] = {1, 0, -1, 0};
  int dw[4] = {0, 1, 0, -1};

  deque<Pii> deq;
  deq.push_back(make_pair(Ch, Cw));
  while (!deq.empty()) {
    int nh = deq.back().first;
    int nw = deq.back().second;
    int nd = SD[nh][nw];
    deq.pop_back();

    rep(i, 4) {
      int nnh = nh + dh[i];
      int nnw = nw + dw[i];
      if (nnh < 0 || nnh >= H || nnw < 0 || nnw >= W)
        continue;
      else if (S[nnh][nnw] == '#')
        continue;
      else if (SD[nnh][nnw] <= nd)
        continue;
      else {
        SD[nnh][nnw] = nd;
        deq.push_back(make_pair(nnh, nnw));
      }
    }

    repm(i, -2, 3) {
      repm(j, -2, 3) {
        int nnh = nh + i;
        int nnw = nw + j;
        if (nnh < 0 || nnh >= H || nnw < 0 || nnw >= W)
          continue;
        else if (S[nnh][nnw] == '#')
          continue;
        else if (SD[nnh][nnw] <= nd + 1)
          continue;
        else {
          SD[nnh][nnw] = nd + 1;
          deq.push_front(make_pair(nnh, nnw));
        }
      }
    }
  }
  cout << (SD[Dh][Dw] == INF ? -1 : SD[Dh][Dw]) << endl;
}

int main() {

  std::ifstream in("input.txt");
  std::cin.rdbuf(in.rdbuf());

  cin.tie(0);
  ios::sync_with_stdio(false);

  input();
  solve();

  return 0;
}


Fixed submission:
#include <algorithm>
#include <bitset>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> Pii;
typedef pair<int, ll> Pil;
typedef pair<ll, ll> Pll;
typedef pair<int, ld> Pid;
typedef pair<int, string> Pis;
#define rep(i, n) for (int i = 0; i < n; i++)
#define repm(i, s, n) for (int i = s; i < n; i++)
#define all(a) (a).begin(), (a).end()

const int INF = 1 << 30;
const ll INF_L = 1LL << 60;
const int MOD = 1e9 + 7; // 998244353;

void coi(ll i) { cout << i << endl; }
void cois(ll i) { cout << i << " "; }
void cod(ld d) {
  cout << fixed << setprecision(16);
  cout << d << endl;
}
void cods(ld d) {
  cout << fixed << setprecision(16);
  cout << d << " ";
}
void coc(char c) { cout << c << endl; }
void cocs(char c) { cout << c << " "; }
void cos(string s) { cout << s << endl; }
void coss(string s) { cout << s << " "; }
void coynl(bool b) { cos(b ? "Yes" : "No"); }
void coYNU(bool b) { cos(b ? "YES" : "NO"); }

// ----------------------------------------------------------------
// String Functions
// ----------------------------------------------------------------
int ctoi(char c) {
  if (isdigit(c))
    return c - '0';
  else if (islower(c))
    return c - 'a';
  else if (isupper(c))
    return c - 'A';
  else
    return -1;
}
char itocd(int i) {
  char c = i + '0';
  if (isdigit(c))
    return c;
  else
    return 0x00;
}
char itocl(int i) {
  char c = i + 'a';
  if (islower(c))
    return c;
  else
    return 0x00;
}
char itocu(int i) {
  char c = i + 'A';
  if (isupper(c))
    return c;
  else
    return 0x00;
}
// ----------------------------------------------------------------

// ----------------------------------------------------------------
// Dynamical Programming
// ----------------------------------------------------------------
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
// ----------------------------------------------------------------

// ----------------------------------------------------------------
// Graph Theory
// ----------------------------------------------------------------
struct edge {
  ll to, cost;
};
struct graph_list {
  ll V;
  vector<vector<edge>> graph;
  vector<ll> dist;

  graph_list(ll n) { init(n); }
  void init(ll n) {
    V = n;
    graph.resize(V);
    dist.resize(V);
    for (int i = 0; i < V; i++) {
      dist[i] = INF_L;
    }
  }
  void add_edge(ll from, ll to, ll cost) {
    edge e;
    e.to = to;
    e.cost = cost;
    graph[from].push_back(e);
  }

  void dijkstra(ll s) {
    for (int i = 0; i < V; i++) {
      dist[i] = INF_L;
    }
    dist[s] = 0;

    priority_queue<Pll, vector<Pll>, greater<Pll>> que;
    que.push(Pll(0, s));
    while (!que.empty()) {
      Pll p = que.top();
      que.pop();
      ll v = p.second;
      if (dist[v] < p.first)
        continue;
      for (auto e : graph[v]) {
        if (dist[e.to] > dist[v] + e.cost) {
          dist[e.to] = dist[v] + e.cost;
          que.push(Pll(dist[e.to], e.to));
        }
      }
    }
  }
  void bellman_ford(ll s) {
    for (int i = 0; i < V; i++) {
      dist[i] = INF_L;
    }
    dist[s] = 0;
  }
};
struct graph_matrix {
  ll vertex;
  vector<vector<edge>> graph;
  vector<ll> dist;

  graph_matrix(ll n) { init(n); }
  void init(ll n) {
    vertex = n;
    graph.resize(vertex);
    dist.resize(vertex);
    for (int i = 0; i < vertex; i++) {
      dist[i] = INF;
    }
  }
  void add_edge(ll s, ll t, ll cost) {
    edge e;
    e.to = t;
    e.cost = cost;
    graph[s].push_back(e);
  }

  void warshall_floyd(ll s) {
    for (int i = 0; i < vertex; i++) {
      dist[i] = INF;
    }
    dist[s] = 0;
  }
};
// ----------------------------------------------------------------

// ----------------------------------------------------------------
// Mathematical Functions
// ----------------------------------------------------------------
ll gcd(ll A, ll B) {
  if (A % B == 0) {
    return (B);
  } else {
    return (gcd(B, A % B));
  }
}
ll lcm(ll A, ll B) { return A * B / gcd(A, B); }

ll getDigit(ll N) { return (ll)(to_string(N).length()); }
ll getDigitForBase(ll N, ll B) {
  if (B < 2) {
    return -1;
  } else if (B == 10) {
    return getDigit(N);
  } else {
    ll r = 0;
    while (N != 0) {
      N /= B;
      r++;
    }
    return r;
  }
}
ll getDivTimes(ll N, ll D) {
  ll r = 0;
  while (N % D == 0) {
    N /= D;
    r++;
  }
  return r;
}

ll powMod(ll B, ll P) {
  if (P == 0)
    return 1;
  if (P % 2 == 0) {
    ll t = powMod(B, P / 2);
    return t * t % MOD;
  }
  return B * powMod(B, P - 1) % MOD;
}

/* ----------------------------------
 Factorial, Permutation, Combination
 ---------------------------------- */
const int FAC_INIT_SIZE = 1e6 + 9;
vector<ll> fac, finv, inv;

void factModInit() {
  fac.resize(FAC_INIT_SIZE);
  finv.resize(FAC_INIT_SIZE);
  inv.resize(FAC_INIT_SIZE);
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < FAC_INIT_SIZE; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}
ll factMod(ll N) { return fac[N] % MOD; }
ll factInvMod(ll N) { return finv[N] % MOD; }
ll permMod(ll N, ll K) {
  if (N < 0 || K < 0 || N < K)
    return 0;
  else
    return factMod(N) * factInvMod(N - K) % MOD;
}
ll combMod(ll N, ll K) {
  if (N < 0 || K < 0 || N < K)
    return 0;
  else if (N < FAC_INIT_SIZE) {
    return factMod(N) * (factInvMod(K) * factInvMod(N - K) % MOD) % MOD;
  } else {
    ll ans = 1;
    ll Ks = K < N - K ? K : N - K;
    for (ll i = N; i > N - Ks; i--) {
      ans *= i;
      ans %= MOD;
    }
    return ans * factInvMod(Ks) % MOD;
  }
}

/* ----------------------------------
 Sieve of Atkin & Bernstein
 ---------------------------------- */
vector<bool> sieve;
void sieveInit(ll size) {
  sieve.clear();
  if (size < 0 || size > INF)
    return;

  int ss = (int)size + 9;
  int ssq = sqrt(ss + 0.1);
  sieve.resize(ss);
  sieve[2] = sieve[3] = true;

  int n = 0;
  for (int z = 1; z <= 5; z += 4) {
    for (int y = z; y <= ssq; y += 6) {
      for (int x = 1; x <= ssq && (n = 4 * x * x + y * y) < ss; x++)
        sieve[n] = !sieve[n];
      for (int x = y + 1; x <= ssq && (n = 3 * x * x - y * y) < ss; x += 2)
        sieve[n] = !sieve[n];
    }
  }
  for (int z = 2; z <= 4; z += 2) {
    for (int y = z; y <= ssq; y += 6) {
      for (int x = 1; x <= ssq && (n = 3 * x * x + y * y) < ss; x += 2)
        sieve[n] = !sieve[n];
      for (int x = y + 1; x <= ssq && (n = 3 * x * x - y * y) < ss; x += 2)
        sieve[n] = !sieve[n];
    }
  }
  for (int z = 1; z <= 2; z++) {
    for (int y = 3; y <= ssq; y += 6) {
      for (int x = z; x <= ssq && (n = 4 * x * x + y * y) < ss; x += 3)
        sieve[n] = !sieve[n];
    }
  }
  for (int k = 5; k <= ssq; k++)
    if (sieve[k])
      for (int n = k * k; n < ss; n += k * k)
        sieve[n] = false;
}

/* ----------------------------------
 Prime Factorization
---------------------------------- */
map<ll, map<ll, ll>> primeFactorMap;
map<ll, set<ll>> primeFactorSet;
void primeFactorizeInit() {
  primeFactorMap.clear();
  primeFactorSet.clear();
}
void primeFactorize(ll N) {
  if (N < 0 || N > INF_L)
    return;

  ll Nc = N, Nsq = sqrt(N + 0.1);
  for (int k = 2; k <= Nsq; k++) {
    ll dt = 0;
    while (Nc % k == 0) {
      dt++;
      Nc /= k;
    }
    if (dt > 0)
      primeFactorMap[N][k] = dt;
    if (N % k == 0) {
      primeFactorSet[N].insert(k);
      primeFactorSet[N].insert(N / k);
    }
  }
  if (Nc != 1)
    primeFactorMap[N][Nc] = 1;
  primeFactorSet[N].insert(1);
  primeFactorSet[N].insert(N);
}
// ----------------------------------------------------------------

//* ****************  GLOBAL VARIABLES  **************** *//
int H, W;
int Ch, Cw;
int Dh, Dw;
vector<string> S;
//* **************************************************** *//

void input() {
  cin >> H >> W;
  cin >> Ch >> Cw;
  Ch--;
  Cw--;
  cin >> Dh >> Dw;
  Dh--;
  Dw--;
  S.resize(H);
  rep(i, H) cin >> S[i];
}

void solve() {

  graph_list g(1000005);
  rep(h, H) {
    rep(w, W) {
      if (S[h][w] == '#')
        continue;
      int ghw = h * H + w;
      if (h != 0)
        g.add_edge(ghw, ghw, 0);
      repm(dh, -2, 3) {
        repm(dw, -2, 3) {
          int nh = h + dh, nw = w + dw;
          int gdhw = nh * H + nw;
          if (nh < 0 || nh >= H || nw < 0 || nw >= W)
            continue;
          if (S[nh][nw] == '#')
            continue;
          if (abs(dh) + abs(dw) == 0)
            continue;
          //                    if(abs(dh) + abs(dw) == 1) g.add_edge(ghw, gdhw,
          //                    0); if(abs(dh) + abs(dw) > 1) g.add_edge(ghw,
          //                    gdhw, 1);
        }
      }
    }
  }
  // g.dijkstra(Ch * H + Cw);
  // coi(g.dist[Dh * H + Dw] == INF_L ? -1 : g.dist[Dh * H + Dw]);

  vector<vector<int>> SD(H, vector<int>(W, INF));
  SD[Ch][Cw] = 0;

  int dh[4] = {1, 0, -1, 0};
  int dw[4] = {0, 1, 0, -1};

  deque<Pii> deq;
  deq.push_back(make_pair(Ch, Cw));
  while (!deq.empty()) {
    int nh = deq.back().first;
    int nw = deq.back().second;
    int nd = SD[nh][nw];
    deq.pop_back();

    rep(i, 4) {
      int nnh = nh + dh[i];
      int nnw = nw + dw[i];
      if (nnh < 0 || nnh >= H || nnw < 0 || nnw >= W)
        continue;
      else if (S[nnh][nnw] == '#')
        continue;
      else if (SD[nnh][nnw] <= nd)
        continue;
      else {
        SD[nnh][nnw] = nd;
        deq.push_back(make_pair(nnh, nnw));
      }
    }

    repm(i, -2, 3) {
      repm(j, -2, 3) {
        int nnh = nh + i;
        int nnw = nw + j;
        if (nnh < 0 || nnh >= H || nnw < 0 || nnw >= W)
          continue;
        else if (S[nnh][nnw] == '#')
          continue;
        else if (SD[nnh][nnw] <= nd + 1)
          continue;
        else {
          SD[nnh][nnw] = nd + 1;
          deq.push_front(make_pair(nnh, nnw));
        }
      }
    }
  }
  cout << (SD[Dh][Dw] == INF ? -1 : SD[Dh][Dw]) << endl;
}

int main() {

  std::ifstream in("input.txt");
  std::cin.rdbuf(in.rdbuf());

  cin.tie(0);
  ios::sync_with_stdio(false);

  input();
  solve();

  return 0;
}