#include <bits/stdc++.h>
// #include <atcoder/all>
using namespace std;
// using namespace atcoder;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep1(i, n) for (int i = 1; i <= (n); i++)
#define rrep(i, n) for (int i = n - 1; i >= 0; i--)
#define rrep1(i, n) for (int i = n; i >= 1; i--)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define eb emplace_back
#define fi first
#define se second
#define sz(x) (int)(x).size()
template <class T> using V = vector<T>;
template <class T> using VV = V<V<T>>;
typedef long long int ll;
// typedef modint998244353 mint;

void speedUpIO() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
}

template <class T> bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
template <class T> bool chmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}
/*--------------------------------------------------*/
typedef pair<int, int> P;
typedef pair<P, P> PP;

const int INF = 1e9;
const ll LINF = 1e18;
const int MX = 1e5;

V<int> dx = {1, 0, -1, 0};
V<int> dy = {0, -1, 0, 1};

void solve() {
    int h, w;
    cin >> h >> w;
    VV<int> a(h, V<int>(w));
    rep(i, h) rep(j, w) cin >> a[i][j];
    V<set<PP>> st(2);
    V<string> col(h, string(w, '.'));
    st[0].insert({{a[0][0], '0'}, {0, 0}});
    st[1].insert({{a[h - 1][w - 1], '1'}, {h - 1, w - 1}});
    int i = 0;
    while (true) {
        auto [p, p2] = *st[i % 2].begin();
        auto [_, c] = p;
        auto [x, y] = p2;
        col[x][y] = c;
        st[i % 2].erase(st[i % 2].begin());
        rep(d, 4) {
            int nx = x + dx[d];
            int ny = y + dy[d];
            if (nx < 0 || nx >= h || ny < 0 || ny >= w) continue;
            if (col[nx][ny] != '.' && col[nx][ny] != col[x][y]) {
                cout << i - 1 << "\n";
                return;
            }
            if (col[nx][ny] != '.') continue;
            st[i % 2].insert({{a[nx][ny], c}, {nx, ny}});
        }
        i++;
    }
}

int main() {
    speedUpIO();
    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
        // cout << solve() << "\n";
        // cout << (solve() ? "Yes" : "No") << "\n";
        // cout << fixed << setprecision(15) << solve() << "\n";
    }
    return 0;
}