#define wiwihorz
#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma loop-opt(on)
#define rep(i, a, b) for(int i = a; i <= b; i ++)
#define rrep(i, a, b) for(int i = b; i >= a; i--)
#define all(x) x.begin(), x.end()
#define ceil(a, b) ((a + b - 1) / (b))
using namespace std;
#define INF 1000000000000000000
#define int long long int
#define pii pair<int, int>
#define random mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count())
#ifdef wiwihorz
#define print(a...) cerr << "Line " << __LINE__ << ": ", kout("[" + string(#a) + "] = ", a)
void vprint(auto L, auto R) { while(L < R) cerr << *L << " \n"[next(L) == R], ++L;}
void kout() { cerr << endl; }
template<class T1, class ... T2> void kout(T1 a, T2 ... e) { cerr << a << " ", kout(e...);}
#else
#define print(...) 0
#define vprint(...) 0
#endif
namespace solver {
int n, m, ans;
vector<vector<int>> a, b;
void init_(int _n, int _m) {
n = _n, m = _m;
a.assign(n + 1, vector<int>(m + 1, 0));
b.assign(n + 1, vector<int>(m + 1, INF));
}
int cal() {
int ans = -INF;
rep(i, 1, n) {
rep(j, 1, m) {
b[i][j] = a[i][j] + 1;
if(i > 1) b[i][j] = min(b[i][j], b[i - 1][j] + 1);
if(j > 1) b[i][j] = min(b[i][j], b[i][j - 1] + 1);
ans = max(ans, a[i][j] - b[i][j]);
}
}
return ans;
}
void solve() {
int ans = -INF;
ans = max(ans, cal());
rep(i, 1, n) rep(j, 1, m) {
if(j <= m / 2) swap(a[i][j], a[i][m - j + 1]);
}
ans = max(ans, cal());
rep(i, 1, n) rep(j, 1, m) {
if(i <= n / 2) swap(a[i][j], a[n - i + 1][j]);
}
ans = max(ans, cal());
rep(i, 1, n) rep(j, 1, m) {
if(j <= m / 2) swap(a[i][j], a[i][m - j + 1]);
}
ans = max(ans, cal());
cout << ans << "\n";
}
};
using namespace solver;
signed main() {
ios::sync_with_stdio(false), cin.tie(0);
int n, m;
cin >> n >> m;
init_(n, m);
rep(i, 1, n) rep(j, 1, m)
cin >> a[i][j];
solve();
return 0;
}
