#include <iostream>
#include <vector>
#include <queue>

using namespace std;

constexpr int iINF = 1'000'000'000;

int main () {
    int H, W; cin >> H >> W;
    vector<vector<int>> A(H, vector<int>(W));
    for (int i = 0; i < H; i++) {
        for (int j = 0; j < W; j++) cin >> A[i][j];
    }

    // グリッド上のダイクストラ法に帰着

    priority_queue<pair<int, pair<int, int>>, vector<pair<int, pair<int, int>>>, greater<pair<int, pair<int, int>>>> pq1, pq2;
    vector<vector<bool>> vis1(H, vector<bool>(W, false)), vis2(H, vector<bool>(W, false));

    pq1.push(make_pair(A[0][0], make_pair(0, 0)));
    pq2.push(make_pair(A[H - 1][W - 1], make_pair(H - 1, W - 1)));

    const vector<pair<int, int>> dxy = {
        make_pair(0, 1),
        make_pair(0, -1),
        make_pair(1, 0),
        make_pair(-1, 0),
    };

    bool end = false;
    int ans = 0;

    while (true) {
        {
            int y, x, c;
            while (true) {
                auto h = pq1.top(); pq1.pop();
                c = h.first;
                y = h.second.first, x = h.second.second;

                if (vis1[y][x]) continue;
                break;
            }
            vis1[y][x] = true;
            ans++;

            for (auto d : dxy) {
                int ny = y + d.first, nx = x + d.second;
                if (!(0 <= ny && ny < H && 0 <= nx && nx < W)) continue;
                if (vis1[ny][nx]) continue;

                // 相手側がもう塗られている
                if (vis2[ny][nx]) {
                    end = true;
                    break;
                }

                pq1.push(make_pair(A[ny][nx], make_pair(ny, nx)));
            }
        }

        if (end) break;

        {
            int y, x, c;
            while (true) {
                auto h = pq2.top(); pq2.pop();
                c = h.first;
                y = h.second.first, x = h.second.second;

                if (vis2[y][x]) continue;
                break;
            }
            vis2[y][x] = true;
            ans++;

            for (auto d : dxy) {
                int ny = y + d.first, nx = x + d.second;
                if (!(0 <= ny && ny < H && 0 <= nx && nx < W)) continue;
                if (vis2[ny][nx]) continue;

                // 相手側がもう塗られている
                if (vis1[ny][nx]) {
                    end = true;
                    break;
                }

                pq2.push(make_pair(A[ny][nx], make_pair(ny, nx)));
            }
        }

        if (end) break;
    }

    cout << ans - 2 << "\n";
}