#include<iostream>
#include<vector>
#include<algorithm>
#include<set>
#include<queue>
using namespace std;
using ll = long long;
using vll = vector<ll>;
using vvll = vector<vll>;
using pll = pair<ll, ll>;
using vpll = vector<pll>;
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
ll n, m;
cin >> n >> m;
vvll matrix(n, vll(m));
for (ll i = 0; i < n; i++) {
for (ll j = 0; j < m; j++) {
cin >> matrix[i][j];
}
}
ll ans = -1;
vvll min_ele(n, vll(m, 1e18));
for (ll i = 0; i < n; i++) {
for (ll j = 0; j < m; j++) {
if (i > 0) {
min_ele[i][j] = min_ele[i - 1][j] + 1;
}
if (j > 0) {
min_ele[i][j] = min(min_ele[i][j - 1] + 1, min_ele[i][j]);
}
min_ele[i][j] = min(min_ele[i][j], matrix[i][j] + 1);
ans = max(ans, matrix[i][j] - min_ele[i][j]);
}
}
vvll max_ele(n, vll(m));
for (ll i = 0; i < n; i++) {
for (ll j = 0; j < m; j++) {
if (i > 0) {
max_ele[i][j] = max_ele[i - 1][j] - 1;
}
if (j > 0) {
max_ele[i][j] = max(max_ele[i][j - 1] - 1, max_ele[i][j]);
}
max_ele[i][j] = max(max_ele[i][j], matrix[i][j] - 1);
ans = max(ans, max_ele[i][j] - matrix[i][j]);
}
}
cout << ans << endl;
}
