#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pll = pair<ll, ll>;
#define drep(i, cc, n) for (ll i = (cc); i <= (n); ++i)
#define rep(i, n) drep(i, 0, n - 1)
#define all(a) (a).begin(), (a).end()
#define pb push_back
#define fi first
#define se second

const ll MOD = 1000000007;
const ll MOD2 = 998244353;
const ll INF = 1LL << 60;
const ll MAX_N = 2e5;

int main(){
    ll n, m;
    cin >> n >> m;

    vector<vector<ll>> d(n, vector<ll>(m));
    rep(i, n) rep(j, m) cin >> d[i][j];
    rep(i, n) sort(all(d[i]));

    ll lw = -1;
    ll hi = 1e9;
    ll mid;
    bool isExist = false;
    while(hi-lw>1){
        mid = (lw+hi)/2;
        
        bool flag = true;
        vector<ll> pre, now;
        rep(j, m) pre.pb(d[0][j]);
        for(ll i=1; i<n; i++){
            now.clear();
            rep(j, m){
                auto itr1 = lower_bound(all(pre), d[i][j]-mid);
                auto itr2 = upper_bound(all(pre), d[i][j]);
                if(itr1 != itr2) now.pb(d[i][j]);
            }

            if((ll)now.size()==0) flag=false;
            swap(pre, now);
        }

        if(flag){
            hi=mid;
            isExist=true;
        }else{
            lw=mid;
        }
    }

    if(isExist) cout << hi << endl;
    else cout << -1 << endl;
}