//////// Wizard_in_Maze 
// https://atcoder.jp/contests/abc176/tasks/abc176_d
// date: 2020-08-22T21:00:10.587610
// memo: 

//<editor-fold desc="my macro">

#include<bits/stdc++.h>

#ifdef LOCAL

#include<my/dump.h>

#else
#define dump(...) 42
#define dumpi(x) 42
#endif

typedef long long ll;
using namespace std;

#define foe(x, a) for(auto& (x) : (a))
#define _overload3(_1, _2, _3, name, ...) name
#define rep(...) _overload3(__VA_ARGS__,_rep3,_rep2,)(__VA_ARGS__)
#define _rep3(i, a, b) for(ll i=a, i##_len=(b);i<i##_len;i++)
#define _rep2(i, n) _rep3(i,0,n)
#define repd(...) _overload3(__VA_ARGS__,_repd3,_repd2,)(__VA_ARGS__)
#define _repd3(i, a, b) for(ll i=b-1, i##_len=(a);i>=i##_len;i--)
#define _repd2(i, n) _repd3(i,0,n)
#define loop(...) _overload3(__VA_ARGS__,,_loop2,_loop1)(__VA_ARGS__)
#define _loop2(i, a) for(ll i=a;; i++)
#define _loop1(i) _loop2(i,0)

#define all(x) x.begin(),x.end()
#define SIZE(x) ((ll)(x).size())

#define pb(a) push_back(a)
#define mp make_pair
#define F first
#define S second
#define vec vector
#define umap unordered_map
#define uset unordered_set

ll dx[24] = {-2, -2, -2, -2, -2, -1, -1, -1, -1, -1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2};
ll dy[24] = {-2, -1, 0, 1, 2, -2, -1, 0, 1, 2, -2, -1, 1, 2, -2, -1, 0, 1, 2, -2, -1, 0, 1, 2};

#define bit(n) (1LL<<(n))
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );

template<class T>
bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}

template<class T>
bool chmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return 1;
    }
    return 0;
}

template<typename T, typename ...Args>
void ci(T &first, Args &... args) {
    ((cin >> first), ..., (cin >> args)); //C++17
}

template<char Sep, typename T, typename ...Args>
void print_seq(const T &first, const Args &... args) {
    ((cout << first), ..., (cout << Sep << args)); //C++17
}

void co() { cout << endl; }

template<typename... Words>
void co(Words... words) {
    print_seq<' '>(words...);
    cout << endl;
}

#define coi(x) cout<<(x)<<" "

#define YES(n) cout << ((n) ? "YES" : "NO"  ) << endl
#define Yes(n) cout << ((n) ? "Yes" : "No"  ) << endl
#define sankou(n, a, b) cout << ((n) ? (#a) : (#b) ) << endl

#define asrt(expr...) assert((expr))

//</editor-fold>

#define INF 1e19
#define MOD 1e9+7
#define MAXR 1000


bool road[MAXR][MAXR];
int loop_n = 0;
bool checked[MAXR][MAXR] = {false};
bool loop_checked[MAXR][MAXR] = {false}; //最短経路用
int close_loop[MAXR][MAXR]{-1};
uset<int> uncheck;
ll H, W;
bool changed = false;

int toPosi(int i, int j) {
    return i*W + j;
}
pair<int,int> toXY(int posi) {
    int x = posi / W;
    int y = posi % W;
    return make_pair(x,y);
}

// i,jマスにlabel_iでラベリングをする。再帰的に隣接もラベリング
void recur(int i, int j, int label_i) {
    if (i < 0 || H <= i) return;
    if (j < 0 || W <= j) return;

    if (road[i][j] == true && checked[i][j] == false) {
        uncheck.insert(toPosi(i, j));
        checked[i][j] = true;
        close_loop[i][j] = label_i;
        recur(i + 1, j, label_i);
        recur(i - 1, j, label_i);
        recur(i, j + 1, label_i);
        recur(i, j - 1, label_i);
    }
}

// ターゲット i,j の 5*5の周りに道があれば、label_i+1でマーク
void recur2(int i, int j, int label_i) {
    rep(dd, 24) {
        int xi = i + dx[dd];
        int xj = j + dy[dd];

        if (xi < 0 || H <= xi) continue;
        if (xj < 0 || W <= xj) continue;

        if (road[xi][xj] == true && checked[xi][xj] == false) {
            changed = true;
            recur(xi, xj, label_i + 1);
        }
    }
}

void recur3(int label_i) {
    vector<int> buf;
    foe(i, uncheck) buf.push_back(i);
    dump(uncheck);

    uncheck.clear();
    foe(i, buf) {
        if (close_loop[toXY(i).F][toXY(i).S] == label_i) {
            recur2(toXY(i).F, toXY(i).S, label_i);
        }
    }
    dump(uncheck);
}

int solve() {
    ci(H, W);
    rep(i, H) rep(j, W) checked[i][j] = false;
    rep(i, H) rep(j, W) loop_checked[i][j] = false;
    rep(i, H) rep(j, W) close_loop[i][j] = -1;

    ll startx, starty;
    ci(startx, starty);
    startx--;
    starty--;
    ll goalx, goaly;
    ci(goalx, goaly);
    goalx--;
    goaly--;
//    dump(startx,starty);
//    dump(goalx,goaly);

    rep(i, H) {
        string s;
        ci(s);
        rep(j, W) {
            if (s[j] == '#') {
                road[i][j] = false;
            } else {
                road[i][j] = true;
            }
//            dump(road[i][j]);
        }
//        dump(s);
    }
//    dump(uncheck);

    // road
//    rep(i,H) {
//        rep(j,W){
//            cout << road[i][j] << " ";
//        }
//        cout << endl;
//    }
//    cout << endl;

//     すべての道に閉路のラベリング
    int xi = startx;
    int xj = starty;

    // 1個ラベリング
    if (road[xi][xj] == true && checked[xi][xj] == false) {
        recur(xi, xj, 0);
        loop_n++; //個数はn+1
    }

    // 一個ラベリングの結果
//    rep(i,H) {
//        rep(j,W){
//            cout << close_loop[i][j] << " ";
//        }
//        cout << endl;
//    }
//    cout << endl;

    loop(i, 0) {
        changed = false;
        recur3(i);
        if (changed == true) continue;
        else break;
    }

    // n個ラベリングの結果
//    rep(i,H) {
//        rep(j,W){
//            cout << close_loop[i][j] << " ";
//        }
//        cout << endl;
//    }
//    cout << endl;

    co(close_loop[goalx][goaly]);

    return 0;
}

int main() {
    //入力の高速化用のコード
    //ios::sync_with_stdio(false);
    //cin.tie(nullptr);

    solve();
    return 0;
}


Measured memory_bytes: 10960