#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll = long long;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using vvvvll = vector<vvvll>;
using vvvvvll = vector<vvvvll>;
using vvvvvvll = vector<vvvvvll>;
using vb = vector<bool>;
using vvb = vector<vb>;
using vvvb = vector<vvb>;
using vvvvb = vector<vvvb>;
using vd = vector<double>;
using vvd = vector<vd>;
using vvvd = vector<vvd>;
using vvvvd = vector<vvvd>;
using vvvvvd = vector<vvvvd>;
#define all(A) A.begin(),A.end()
#define ALL(A) A.begin(),A.end()
#define rep(i, n) for (ll i = 0; i < (ll) (n); i++)
using pqr = priority_queue<pair<ll, ll>, vector<pair<ll, ll>>, greater<pair<ll, ll>>>;


template<class T>
bool chmax(T& p, T q, bool C = 1) {
    if (C == 0 && p == q) {
        return 1;
    }
    if (p < q) {
        p = q;
        return 1;
    }
    else {
        return 0;
    }
}

template<class T>
bool chmin(T& p, T q, bool C = 1) {
    if (C == 0 && p == q) {
        return 1;
    }
    if (p > q) {
        p = q;
        return 1;
    }
    else {
        return 0;
    }
}

ll gcd(ll(a), ll(b)) {
    if (a == 0)return b;
    if (b == 0)return a;
    ll c = a;
    while (a % b != 0) {
        c = a % b;
        a = b;
        b = c;
    }
    return b;
}
ll sqrtz(ll N) {
    ll L = 0;
    ll R = sqrt(N) + 10000;
    while (abs(R - L) > 1) {
        ll mid = (R + L) / 2;
        if (mid * mid <= N)L = mid;
        else R = mid;
    }
    return L;

}

/*
using mint = modint998244353;
//using Mint = modint;
vector<mint> fact, factinv, inv;
const ll mod = 998244353;
void prenCkModp(ll n) {
    fact.resize(n + 5);
    factinv.resize(n + 5);
    inv.resize(n + 5);
    fact[0] = fact[1] = 1;
    factinv[0] = factinv[1] = 1;
    inv[1] = 1;
    for (ll i = 2; i < n + 5; i++) {
        fact[i] = (fact[i - 1] * i);
        inv[i] = mod - (inv[mod % i] * (mod / i));
        factinv[i] = (factinv[i - 1] * inv[i]);
    }

}

mint nCk(ll n, ll k) {
    if (n < k || k < 0) return 0;
    return fact[n] * (factinv[k] * factinv[n - k]);
}
*/

template<class T>
vector<vector<T>> mul(vector<vector<T>> A, vector<vector<T>> B) {
    ll N = A.size();
    vector<vector<T>> res(N, vector<T>(N, 0));
    rep(i, N)rep(j, N)rep(k, N) {
        res[i][j] += A[i][k] * B[k][j];
    }
    return res;
}

using mint = modint998244353;

int main() {

    ll N, M;
    cin >> N >> M;
    vvll D(N, vll(M));
    rep(i, N) {
        rep(j, M)cin >> D[i][j];
        sort(all(D[i]));
    }

    ll L = -1, R = 1e10;
    while (R - L > 1) {
        ll mid = (R + L) / 2;
        vvb DP(N, vb(M, 0));
        rep(i, M)DP[0][i] = 1;


        for (ll i = 1; i < N; i++) {
            vll OK;
            rep(j, M)if (DP[i - 1][j])OK.push_back(D[i - 1][j]);
            if (OK.size() == 0)break;
            rep(j, M) {
                auto p = upper_bound(all(OK), D[i][j]);
                p--;
                auto q = lower_bound(all(OK), D[i][j] - mid);
                if (ll(p-OK.begin()) >=  ll(q-OK.begin())) {
                    DP[i][j] = 1;
                }

            }
        }
        bool E = 0;
        rep(i, M) {
            if (DP[N - 1][i]) {
                R = mid;
                E = 1;
            }
        }
        if (!E)L = mid;

    }
    cout << (R < 1e10 - 5 ? R : -1) << endl;
}