#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define N 600005
#define pb push_back
#define ff first
#define ss second
#define all(x) x.begin(),x.end()
#define sz(s) (int)s.size()
#define pii pair<int,int>
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ll T, n, a[2000][2000], t, m, answer;
int main () {
ios::sync_with_stdio(0);cin.tie(0);
cin >> n >> m;
for(int i = 1;i <= n;i++) {
for(int j = 1;j <=m;j++) {
cin >> a[i][j];
}
}
for(int i = 1; i <= m; i++) {
ll mn = a[1][i], mx = a[1][i];
for(int j = i + 1; j <= m; j++) {
mx = max(mx,a[1][j]);
mn = min(mn,a[1][j]);
answer = max(answer, mx - mn - (j - i + 1));
}
}
cout << answer << '\n';
}
