#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define s second
#define f first
#define pb push_back
#define ep emplace
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define uniquev(v) sort(all(v)), (v).resize(unique(all(v)) - (v).begin())
#define mem(f,x) memset(f , x , sizeof(f))
#define sz(x) (int)(x).size()
#define __lcm(a, b) (1ll * ((a) / __gcd((a), (b))) * (b))
#define mxx *max_element
#define mnn *min_element
#define cntbit(x) __builtin_popcountll(x)
#define len(x) (int)(x.length())
const int N = 1e3 + 10;
int a[N][N], mx[N][N];
int n, m;
int cal() {
for (int i = 0; i <= n; i++) {
for (int j = 0; j <= m; j++) {
mx[i][j] = 2e9;
}
}
int ans = -1;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
int v = a[i][j] - i - j;
mx[i][j] = min({mx[i][j - 1], mx[i - 1][j], v});
ans = max(ans, v - mx[i][j] - 1);
}
}
return ans;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> n >> m;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
cin >> a[i][j];
}
}
int ans = cal();
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m / 2; j++) {
swap(a[i][j], a[i][m - j + 1]);
}
}
ans = max(ans, cal());
for (int i = 1; i <= n / 2; i++) {
for (int j = 1; j <= m; j++) {
swap(a[i][j], a[n - i + 1][j]);
}
}
ans = max(ans, cal());
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m / 2; j++) {
swap(a[i][j], a[i][m - j + 1]);
}
}
ans = max(ans, cal());
cout << ans << '\n';
return 0;
}
// a[x][y] - a[x1][y1] - (x - x1) - (y - y1)
// a[x][y] - a[x1][y1] - x + x1 - y + y1
// a[x][y] - x - y - (a[x1][y1] - x1 - y1)
