/**
* In the name of Allah
* We are nothing and you're everything
* author: najmuddin
**/
#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
using namespace std;
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
#define int ll
const char nl = '\n';
const int N = 1e8+5;
//const int inf = 1e18;
const int mod = 1e9+7;
void solve() {
int ans = -1;
int n, m; cin >> n >> m;
vector<vector<int>> dp(n+1, vector<int> (m+1));
vector<vector<int>> a(n, vector<int> (m));
for (int i = 0; i < n; ++i)
for (int j = 0; j < m; ++j)cin >> a[i][j];
// vpravo
for (int i = 0; i < n; ++i)
for (int j = 0; j < m; ++j) {
dp[i][j] = a[i][j]+1;
if (j > 0)dp[i][j] = min(dp[i][j-1]+1, dp[i][j]);
}
//vlevo
for (int i = 0; i < n; ++i)
for (int j = m-1; j >= 0; --j) {
dp[i][j] = min(dp[i][j], a[i][j]+1);
if (j < m-1)dp[i][j] = min(dp[i][j], dp[i][j+1]+1);
}
//vverh
for (int j = 0; j < m; ++j)
for (int i = n-1; i >= 0; --i) {
dp[i][j] = min(dp[i][j], a[i][j]+1);
if (i < n-1)dp[i][j] = min(dp[i][j], dp[i+1][j]+1);
}
//vniz
for (int j = 0; j < m; ++j) {
for (int i = 0; i < n; ++i) {
dp[i][j] = min(dp[i][j], a[i][j]+1);
if (i > 0)
dp[i][j] = min(dp[i][j], dp[i-1][j]+1);
}
}
for (int i = 0; i < n; ++i)
for (int j = 0; j < m; ++j)
ans = max(ans, a[i][j]-dp[i][j]);
cout << ans;
}
int32_t main() {
ios::sync_with_stdio(0);
cin.tie(0);
int t = 1;
//cin >> t;
while (t--) {
solve();
}
return 0;
}
