#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define run ios_base::sync_with_stdio(false);cin.tie(0);
#define ln length()
#define ll long long
#define pll pair<ll, ll>
#define ull unsigned ll
#define ld double
#define endl "\n"
#define pb push_back
#define fi first
#define se second
#define pi acos(-1)
#define N 1007
#define INF 10000000000
#define minimum -9223372036854775807
#define maximum -minimum
#define mod 1000000007
using namespace std;
using namespace __gnu_pbds;
template <class t>
using ordered_set=tree<t, null_type,less_equal<t>, rb_tree_tag,tree_order_statistics_node_update>;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ll gcd(ll a, ll b)
{
if(b==0)
return a;
return gcd(b, a%b);
}
ll lcm(ll a, ll b)
{
return a/gcd(a, b)*b;
}
bool isprime(ll n)
{
if(n==1)
return 0;
for(ll i=2; i*i<=n; i++)
{
if(n%i==0)
return 0;
}
return 1;
}
ll binpow(ll a, ll b)
{
a%=mod;
ll res=1;
while(b>0)
{
if(b%2==1)
res=(res*a)%mod;
a=(a*a)%mod;
b/=2;
}
return res;
}
ll n, m;
ll a[N][N];
pll t[N];
void build(ll node, ll l, ll r)
{
if(l==r)
{
t[node].first=a[1][l];
t[node].second=a[1][l];
return;
}
ll mid=(l+r)/2;
build(node*2, l, mid);
build(node*2+1, mid+1, r);
t[node].first=min(t[node*2].first, t[node*2+1].first);
t[node].second=max(t[node*2].second, t[node*2+1].second);
}
pll get(ll node, ll l, ll r, ll ql, ll qr)
{
if(qr<l || r<ql)
return {maximum, minimum};
if(ql<=l && r<=qr)
return t[node];
ll mid=(l+r)/2;
pll res1=get(node*2, l, mid, ql, qr);
pll res2=get(node*2+1, mid+1, r, ql, qr);
return {min(res1.first, res2.first), max(res1.second, res2.second)};
}
int main()
{
run;
cin>>n>>m;
for(ll i=1; i<=n; i++)
{
for(ll j=1; j<=m; j++)
{
cin>>a[i][j];
}
}
ll cvb=0;
if(n==1)
{
build(1, 1, m);
for(ll i=1; i<=m; i++)
{
for(ll j=i; j<=m; j++)
{
pll res=get(1, 1, m, i, j);
if(cvb<res.second-res.first-(j-i+1))
{
cvb=max(cvb, res.second-res.first-(j-i+1));
// cout<<i<<" "<<j<<endl;
}
}
}
cout<<cvb<<endl;
}
else
{
ll sz=n*m;
vector<ll>v(sz+1, 0);
ll idx=1;
for(ll i=1; i<=n; i++)
{
for(ll j=1; j<=m; j++)
{
v[idx]=a[i][j];
idx++;
}
}
for(ll mask=0; mask<(1<<sz); mask++)
{
ll num=0, minn=maximum, maxx=minimum;
for(ll i=1; i<=sz; i++)
{
if((1<<mask)&i)
{
num++;
minn=min(minn, v[i]);
maxx=max(maxx, v[i]);
}
}
cvb=max(cvb, maxx-minn-num);
}
cout<<cvb<<endl;
}
}
// By Xanlar
