#include <bits/stdc++.h>

using namespace std;

#define int long long
#define FOR(i, a, b) for(ll i = (a); i < (b); ++i)
#define FORR(i, a, b) for(ll i = (a); i > (b); --i)
#define REP(i, n) for(ll i = 0; i < (n); ++i)
#define REPR(i, n) for(ll i = n; i >= 0; i--)
#define FOREACH(x, a) for(auto &(x) : (a))
#define VECCIN(x)                                                              \
    for(auto &youso_ : (x)) cin >> youso_
#define mp make_pair
#define bitcnt __builtin_popcount
#define SZ(x) ((ll)(x).size())
#define All(a) (a).begin(), (a).end()
template <typename T = long long> inline T IN() {
    T x;
    cin >> x;
    return (x);
}
inline void CIN() {}
template <class Head, class... Tail>
inline void CIN(Head &&head, Tail &&... tail) {
    cin >> head;
    CIN(move(tail)...);
}
#define CINT(...)                                                              \
    int __VA_ARGS__;                                                           \
    CIN(__VA_ARGS__)
#define LCIN(...)                                                              \
    ll __VA_ARGS__;                                                            \
    CIN(__VA_ARGS__)
#define SCIN(...)                                                              \
    string __VA_ARGS__;                                                        \
    CIN(__VA_ARGS__)
#define Yes(a) cout << (a ? "Yes" : "No") << "\n"
#define YES(a) cout << (a ? "YES" : "NO") << "\n"
#define Printv(v)                                                              \
    {                                                                          \
        FOREACH(x, v) { cout << x << " "; }                                    \
        cout << "\n";                                                          \
    }
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
    std::fill((T *)array, (T *)(array + N), val);
}

typedef long long ll;
typedef unsigned long long ul;
typedef vector<ll> VL;
typedef pair<ll, ll> PL;
typedef priority_queue<ll> PQ;
typedef priority_queue<ll, VL, greater<ll>> PQG;

const int INF = 1e9;
const int MOD = 1e9 + 7;
// const int MOD = 998244353;
const ll LINF = 1e18;
const ll dx[] = {1, -1, 0, 0};
const ll dy[] = {0, 0, 1, -1};

signed main() {
    while(1) {
        int d, w;
        int ans = 0;
        cin >> d >> w;
        if(d == 0 && w == 0) {
            break;
        }
        vector<vector<int>> A(d, vector<int>(w));
        REP(i, d) REP(j, w) cin >> A[i][j];
        FOR(ds, 0, d - 2) FOR(de, ds + 2, d) {
            FOR(ss, 0, w - 2) FOR(se, ss + 2, w) {
                bool ok = true;
                int tmp = 0;
                int mn = 1e9;
                FOR(x, ds, de + 1) {
                    mn = min(mn, A[x][ss]);
                    mn = min(mn, A[x][se]);
                }
                FOR(y, ss, se + 1) {
                    mn = min(mn, A[ds][y]);
                    mn = min(mn, A[de][y]);
                }
                FOR(y, ss, se + 1) FOR(x, ds, de + 1) {
                    if(x == ds || x == de || y == ss || y == se) {
                        continue;
                    }
                    if(A[x][y] >= mn) {
                        ok = false;
                        break;
                    }
                    tmp += mn - A[x][y];
                }
                if(!ok) continue;
                ans = max(tmp, ans);
            }
        }
        cout << ans << endl;
    }
}


Measured memory_bytes: 3140