#include <bits/stdc++.h>
#define respagold ios_base::sync_with_stdio(0), cin.tie(0);
#define ll long long
#define int long long
#define int2 __int128_t
#define FOR( i, x, n, d ) for( int i = x; i <= n; i += d )
#define FORR( i, x, n, d ) for( int i = x; i >= n; i -= d )
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x.size())
#define pb push_back
#define ins insert
#define lb lower_bound
#define ub upper_bound
#define pii pair <int, int>
#define mkp make_pair
using namespace std;
const int N = 1e6 + 123;
const int inf = 2e18;
const int MOD = 1e9 + 7;
const int MOD1 = 998244353;
const int P = 6547;
int a[N], b[N], c[N], n, m, x, y, z, w;
int mz[N];
mt19937 rng( chrono::steady_clock::now().time_since_epoch().count());
int rand( int l, int r )
{
uniform_int_distribution <int> uid( l, r );
return uid( rng );
}
bool valid( int x, int y )
{
if( x < 1 || x > n || y < 1 || y > m ) return 0;
return 1;
}
int calc( int x, int y )
{
return (x - 1) * m + y;
}
bool check( int x, int y )
{
int xy = x % m, yy = y % m; xy = ( xy == 0 ? m : xy ), yy = ( yy == 0 ? m : yy );
int xx = ( x - xy ) / m + 1, yx = ( y - yy ) / m + 1;
if( xx == yx ) return ( abs( xy - yy ) <= 1 );
if( xy == yy ) return ( abs( xx - yx ) <= 1 );
return 0;
}
void solve()
{
cin >> n >> m;
int ans = 0;
FOR( i, 1, n, 1 )
{
FOR( j, 1, m, 1 )
{
cin >> mz[calc(i, j)];
}
}
FOR( mask, 0, (1 << n * m) - 1, 1 )
{
int mn = inf, mx = -inf, cnt = 0;
int lst = -1, ok = 1;
FOR( i, 0, n * m - 1, 1 )
{
if( (mask >> i) & 1 )
{
if( lst != -1 && !check( lst, i + 1 ) ) ok = 0;
lst = i + 1;
mn = min( mn, mz[i + 1] );
mx = max( mx, mz[i + 1] );
cnt ++;
}
}
if(ok) ans = max( ans, mx - mn - cnt );
}
cout << ans;
}
signed main()
{
// freopen("connect.in", "r", stdin);
// freopen("connect.out", "w", stdout);
respagold
int test = 1;
if( !test ) cin >> test;
while( test -- )
{
solve();
}
}
// solved by KluydQ
