#include "bits/stdc++.h"
using namespace std;
void solve() {
int n, m;
cin >> n >> m;
vector<vector<int>> a(n, vector<int> (m)), dp(n, vector<int> (m));
using T = array<int, 3>;
priority_queue<T> tmp;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
cin >> a[i][j];
dp[i][j] = a[i][j] - 1;
tmp.push({dp[i][j], i, j});
}
}
while (!tmp.empty()) {
auto [value, x, y] = tmp.top();
tmp.pop();
if (dp[x][y] != value) {
continue;
}
for (auto [x2, y2] : vector<pair<int, int>> {{x - 1, y}, {x + 1, y}, {x, y - 1}, {x, y + 1}}) {
if (x2 >= 0 && y2 >= 0 && x2 < n && y2 < m && dp[x2][y2] < value - 1) {
dp[x2][y2] = value - 1;
tmp.push({dp[x2][y2], x2, y2});
}
}
}
int ans = -1;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
ans = max(ans, dp[i][j] - a[i][j]);
}
}
cout << ans << '\n';
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
}
