#include <bits/stdc++.h>
#ifdef local
#define debug(args...) qqbx(#args, args)
#define safe cerr<<__PRETTY_FUNCTION__<<" line "<<__LINE__<<" safe\n"
template <typename ...T> void qqbx(const char *s, T ...args) {
int cnt = sizeof...(T);
(std::cerr << "(" << s << ") = (" , ... , (std::cerr << args << (--cnt ? ", " : ")\n")));
}
#else
#define debug(...) ((void)0)
#define safe ((void)0)
#endif // local
#define all(v) begin(v),end(v)
using namespace std;
signed main() {
ios_base::sync_with_stdio(0), cin.tie(0);
int n, m;
cin >> n >> m;
vector<vector<int>> v(n, vector<int>(m));
for(int i = 0; i < n; i++) for(int j = 0; j < m; j++) cin >> v[i][j];
vector<vector<int>> dp(n, vector<int>(m));
int best = -1e9;
auto calc = [&]() {
for(int i = 0; i < n; i++) {
for(int j = 0; j < m; j++) {
dp[i][j] = v[i][j];
if(i) dp[i][j] = max(dp[i][j], dp[i-1][j] - 1);
if(j) dp[i][j] = max(dp[i][j], dp[i][j-1] - 1);
best = max(best, dp[i][j] - v[i][j] - 1);
}
}
};
calc();
reverse(all(v));
calc();
for(auto &u: v) reverse(all(u));
calc();
reverse(all(v));
calc();
cout << best << '\n';
}
