#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define repk(i, k, n) for (int i = k; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
#define mod3 100000007
#define vi vector<int>
#define vs vector<string>
#define vc vector<char>
#define vl vector<ll>
#define vvi vector<vector<int>>
#define vvc vector<vector<char>>
#define vvl vector<vector<ll>>
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define pii pair<int,int>
#define pil pair<int,ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpii vector<pair<int,int>>
#define vpll vector<pair<ll,ll>>
#define vvpii vector<vector<pair<int,int>>>
#define vvpll vector<vector<pair<ll,ll>>>

template<typename T> void debug(T e){
    cerr << e << endl;
}

template<typename T> void debug(vector<T> &v){
    rep(i, v.size()){
        cerr << v[i] << " ";
    }
    cerr << endl;
}

template<typename T> void debug(vector<vector<T>> &v){
    rep(i, v.size()){
        rep(j, v[i].size()){
            cerr << v[i][j] << " ";
        }
        cerr << endl;
    }
}

template<typename T> void debug(vector<pair<T, T>> &v){
    rep(i,v.size()){
        cerr << v[i].first << " " << v[i].second << endl;
    }
}

template<typename T> void debug(set<T> &st){
    for (auto itr = st.begin(); itr != st.end(); itr++){
        cerr << *itr << " ";
    }
    cerr << endl;
}

template<typename T> void debug(multiset<T> &ms){
    for (auto itr = ms.begin(); itr != ms.end(); itr++){
        cerr << *itr << " ";
    }
    cerr << endl;
}

template<typename T> void debug(map<T, T> &mp){
    for (auto itr = mp.begin(); itr != mp.end(); itr++){
        cerr << itr->first << " " << itr->second << endl;
    }
}

void debug_out(){
    cerr << endl;
}

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T){
    cerr << H << " ";
    debug_out(T...);
}

bool judge(vector<vector<ll>> &D, ll N, ll M, ll center){
    //差をcenter以下にできるか？
    bool ret = false;
    vector<ll> can(0);
    rep(j,M){
        can.push_back(D[0][j]);
    }
    for (ll i = 0; i < N - 1; i++){
        vector<bool> pos(M, false);
        for (ll j = 0; j < M; j++){
            if (can.size() == 0){
                break;
            }
            else if (can[0] > D[i + 1][j]){
                continue;
            }
            else if (can[can.size() - 1] < D[i + 1][j] - center){
                continue;
            }
            else{
                auto itr = lower_bound(all(can), D[i + 1][j] - center);
                if (*itr <= D[i + 1][j]){
                    pos[j] = true;
                }
            }
        }
        can.clear();
        for (ll j = 0; j < M; j++){
            if (pos[j]) can.push_back(D[i + 1][j]);
        }
        //debug(can);
    }
    if (can.size() >= 1){
        ret = true;
    }
    return ret;
}

int main(){
    ll N,M;
    cin >> N >> M;
    vvl D(N, vl(M));
    rep(i,N){
        rep(j,M){
            cin >> D[i][j];
        }
    }
    rep(i,N){
        sort(all(D[i]));
    }
    if (N == 1){
        cout << 0 << endl;
        return 0;
    }
    ll left = -1;
    ll right = 1000000001;
    while(right - left > 1){
        ll center = (left + right) / 2;
        if (judge(D, N, M, center)){
            right = center;
        }
        else{
            left = center;
        }
    }
    if (right == 1000000001){
        cout << -1 << endl;
    }
    else{
        cout << right << endl;
    }
}