#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int INF = (int) 1e9 + 1e6 + 123;
const ll LINF = (ll) 1e18 + 1e9 + 123;
#define rep(i, s, t) for (auto i = (s); i < (t); ++(i))
#define per(i, s, t) for (auto i = (s); i >= (t); --(i))
#define sz(x) ((int)(x).size())
#define mp make_pair
#define pb push_back
bool mini(auto &x, const auto &y) {
if (y < x) {
x = y;
return 1;
}
return 0;
}
bool maxi(auto &x, const auto &y) {
if (y > x) {
x = y;
return 1;
}
return 0;
}
void run();
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
run();
return 0;
}
const int N = (int) 1000 + 1;
int n, m;
int a[N][N], dp[N][N];
bool vis[N][N];
const int dx[4] = {-1, 1, 0, 0};
const int dy[4] = {0, 0, -1, 1};
void run() {
cin >> n >> m;
rep(i, 0, n) {
rep(j, 0, m) {
cin >> a[i][j];
}
}
priority_queue<pair<int, pair<int, int>>> q;
rep(i, 0, n) {
rep(j, 0, m) {
dp[i][j] = a[i][j] + 1;
q.push({-(a[i][j] + 1), {i, j}});
}
}
while (sz(q)) {
auto it = q.top();
int i = it.second.first;
int j = it.second.second;
q.pop();
if (vis[i][j]) continue;
vis[i][j] = 1;
rep(dir, 0, 4) {
int ni = i + dx[dir];
int nj = j + dy[dir];
if (mini(dp[ni][nj], dp[i][j] + 1)) {
q.push({-dp[ni][nj], {ni, nj}});
}
}
}
int ans = 0;
rep(i, 0, n) rep(j, 0, m) maxi(ans, a[i][j] - dp[i][j]);
cout << ans << "\n";
}
