#ifdef LOCAL
#include <iostream>
#include <fstream>
#include <iomanip>
#include <cassert>
#include <random>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#else
#pragma GCC optimize("Ofast,unroll-loops")
#include <bits/stdc++.h>
#define cerr if (false) cerr
#define endl '\n'
#endif
#define fi first
#define se second
#define sz(a) ((int)(a).size())
#define all(a) (a).begin(), (a).end()
#define lsb(x) (x & (-x))
#define bit(mask, i) (((mask) >> (i)) & 1)
#define popcount(x) __builtin_popcount(x)
#define YES cout << "YES" << endl
#define NO cout << "NO" << endl
using namespace std;
template <typename T>
bool ckmax(T &a, T b) { return a < b ? a = b, true : false; }
template <typename T>
bool ckmin(T &a, T b) { return a > b ? a = b, true : false; }
using ll = long long;
using pii = pair<int, int>;
const int NMAX = 1005;
const int INF = 1e9+5;
int n, m;
int a[NMAX][NMAX];
int dp[NMAX][NMAX];
void read() {
cin >> n >> m;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++)
cin >> a[i][j];
}
}
void reset() {
for (int i = 0; i <= n + 1; i++)
fill(dp[i], dp[i] + m + 2, INF);
}
int solve() {
int ans = -1;
reset();
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
dp[i][j] = a[i][j] + 1;
ckmin(dp[i][j], min(dp[i - 1][j], dp[i][j - 1]) + 1);
ckmax(ans, a[i][j] - dp[i][j]);
}
}
reset();
for (int i = 1; i <= n; i++) {
for (int j = m; j >= 1; j--) {
dp[i][j] = a[i][j] + 1;
ckmin(dp[i][j], min(dp[i - 1][j], dp[i][j + 1]) + 1);
ckmax(ans, a[i][j] - dp[i][j]);
}
}
reset();
for (int i = n; i >= 1; i--) {
for (int j = 1; j <= m; j++) {
dp[i][j] = a[i][j] + 1;
ckmin(dp[i][j], min(dp[i + 1][j], dp[i][j - 1]) + 1);
ckmax(ans, a[i][j] - dp[i][j]);
}
}
reset();
for (int i = n; i >= 1; i--) {
for (int j = m; j >= 1; j--) {
dp[i][j] = a[i][j] + 1;
ckmin(dp[i][j], min(dp[i + 1][j], dp[i][j + 1]) + 1);
ckmax(ans, a[i][j] - dp[i][j]);
}
}
return ans;
}
signed main() {
#ifdef LOCAL
freopen("input.txt", "r", stdin);
#endif
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int t = 1;
// cin >> t;
while (t--) {
read();
cout << solve() << endl;
}
return 0;
}
