#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <utility>
#include <vector>
#define rep(i, n) for (int i = 0, i##_len = (n); i < i##_len; ++i)
#define reps(i, n) for (int i = 1, i##_len = (n); i <= i##_len; ++i)
#define rrep(i, n) for (int i = ((int)(n)-1); i >= 0; --i)
#define rreps(i, n) for (int i = ((int)(n)); i > 0; --i)
#define INF 1000000000
#define MOD 1000000007
#define CHOOSE(a) CHOOSE2 a
#define CHOOSE2(a0, a1, a2, a3, a4, x, ...) x
#define debug_1(x1) cout << #x1 << ": " << x1 << endl
#define debug_2(x1, x2) \
    cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << endl
#define debug_3(x1, x2, x3)                                                 \
    cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": " \
         << x3 << endl
#define debug_4(x1, x2, x3, x4)                                             \
    cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": " \
         << x3 << ", " #x4 << ": " << x4 << endl
#define debug_5(x1, x2, x3, x4, x5)                                         \
    cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": " \
         << x3 << ", " #x4 << ": " << x4 << ", " #x5 << ": " << x5 << endl
#ifdef _DEBUG
#define debug(...)                                                        \
    CHOOSE((__VA_ARGS__, debug_5, debug_4, debug_3, debug_2, debug_1, ~)) \
    (__VA_ARGS__)
#else
#define debug(...)
#endif

using namespace std;
using ll = long long;
typedef pair<int, int> P;

int dx[4] = {1, -1, 0, 0}, dy[4] = {0, 0, 1, -1};

int main() {
    int sy, sx, gy, gx;
    int r, c;
    cin >> r >> c >> sy >> sx >> gy >> gx;
    sy--, sx--, gy--, gx--;
    vector<string> field(r);
    vector<vector<int>> cost(r, vector<int>(c, INF));
    rep(i, r) cin >> field[i];

    queue<P> que, visited;
    que.push(P(sy, sx));
    cost[sy][sx] = 0;

    while (!que.empty() || !visited.empty()) {
        if (!que.empty()) {
            P p = que.front();
            visited.push(P(p.first, p.second));
            que.pop();

            // 4方向探索
            rep(i, 4) {
                int ny = dy[i] + p.first;
                int nx = dx[i] + p.second;

                //移動可能か判断
                if (0 > nx || nx >= c || 0 > ny || ny >= r ||
                    field[ny][nx] == '#')
                    continue;

                if (cost[ny][nx] > cost[p.first][p.second]) {
                    cost[ny][nx] = cost[p.first][p.second];
                    que.push(P(ny, nx));
                }
            }
        } else {
            P p = visited.front();
            visited.pop();
            for (int jy = -2; jy <= 2; ++jy) {
                for (int ix = -2; ix <= 2; ++ix) {
                    int ny = jy + p.first;
                    int nx = ix + p.second;

                    if (0 > nx || nx >= c || 0 > ny || ny >= r ||
                        field[ny][nx] == '#')
                        continue;

                    if (cost[ny][nx] > cost[p.first][p.second] + 1) {
                        cost[ny][nx] = cost[p.first][p.second] + 1;
                        que.push(P(ny, nx));
                    }
                }
            }
        }
    }

    if (cost[gy][gx] == INF)
        cout << -1 << endl;
    else
        cout << cost[gy][gx] << endl;

    return 0;
}

Measured memory_bytes: 8556