#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<ll,ll>;
#define fix(x) fixed << setprecision(x)
#define asc(x) x, vector<x>, greater<x>
#define rep(i, n) for(ll i = 0; i < n; i++)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}
constexpr ll INFLL = (1LL <<62);
constexpr int INF = 2e9;
int dp[1500][1500];

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n,m;
    cin >> n >> m;
    vector<vector<int>> a(1500, vector<int>(1500));
    rep(i,n){
        rep(j,m){
            cin >> a[i][j];
            dp[i][j] = INF;
        }
    }
    rep(i,m) dp[0][i] = 0;
    rep(i,n-1){
        rep(j,m){
            rep(k,m){
                if(a[i+1][j]<a[i][k]) continue;
                chmin(dp[i+1][j], max(a[i+1][j]-a[i][k], dp[i][k]));
            }
        }
    }
    int ans = INF;
    rep(i,m) chmin(ans, dp[n-1][i]);
    if(ans==INF) ans = -1;
    cout << ans << '\n';
    return 0;
}