#include <vector>
#include <list>
#include <map>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <queue>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <fstream>
#include <cstdio>
#include <climits>
#include <complex>
#include <cstdint>
#include <tuple>

#define M_PI       3.14159265358979323846

using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v; }
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); }
inline int readInt() { int x; scanf("%d", &x); return x; }

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef unsigned long long ULL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;

//container util

//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define SQ(a) ((a)*(a))
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,s,n) for(int i=s;i<(int)n;++i)
#define REP(i,n) FOR(i,0,n)
#define MOD 1000000007

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define trav(a, x) for(auto& a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()
struct Edge {
    int to, cost;
    Edge(int to, int cost): to(to), cost(cost) {}
};

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vector<Edge>> AdjList;
AdjList graph;

const int INF = 100000000;



map<int, char> mp;

int t[10010];
int main() {
    //cout << fixed << setprecision(15);

    int d, w;
    while(cin >> d >> w){
        if(d == 0 && w == 0) break;

        vector<vector<int>> v(15);
        REP(i, d){
            REP(j, w){
                int a = readInt();
                v[i].push_back(a);
            }
        }

        int maxV = 0;
        for(int ly=0; ly<d; ++ly){
            for(int lx = 0; lx<w; ++lx){
                for(int ry = ly+1; ry<d; ++ry){
                    for(int rx = lx+1; rx<w; ++rx){
                        int minV = 10000;
                        for(int i=ly; i<=ry; ++i){
                            minV = min(minV, v[i][lx]);
                            minV = min(minV, v[i][rx]);
                        }

                        for(int i=lx; i<=rx; ++i){
                            minV = min(minV, v[ly][i]);
                            minV = min(minV, v[ry][i]);
                        }
                        //cout << minV << endl;
                        int cnt=0;
                        bool c = true;
                        for(int i=ly+1; i<=ry-1; ++i){
                            for(int j=lx+1; j<=rx-1; ++j){
                                if(v[i][j] >= minV){
                                    c = false;
                                }
                                cnt += max(0, minV - v[i][j]);
                            }
                        }
                        if(!c) continue;
                        maxV = max(maxV, cnt);
                    }
                }
            }
        }
        cout << maxV << endl;
    }
    return 0;
}


Measured memory_bytes: 3216