#include <algorithm>
#include <iostream>
#include <iomanip>
#include <limits.h>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <utility>
#include <vector>
#include <stack>
#include <complex>

using namespace std;
#define rep(i, n) for (int i = 0; i < n; i++)
#define rep1(i, n) for (int i = 1; i < n + 1; i++)
#define rev(i, n) for (int i = n - 1; i >= 0; i--)
#define all(A) A.begin(), A.end()
#define itr(A, l, r) A.begin() + l, A.begin() + r
#define debug(var) cout << #var << " = " << var << endl;
typedef long long ll;

template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p)
{
    os << "(" << p.first << "," << p.second << ")";
    return os;
}

template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p)
{
    is >> p.first >> p.second;
    return is;
}

template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v)
{
    for (int i = 0; i < (int)v.size(); i++)
    {
        os << v[i] << (i + 1 != (int)v.size() ? " " : "");
    }
    return os;
}

template <typename T>
ostream &operator<<(ostream &os, const vector<vector<T>> &v)
{
    for (int i = 0; i < (int)v.size(); i++)
    {
        os << v[i] << endl;
    }
    return os;
}

template <typename T>
ostream &operator<<(ostream &os, const vector<vector<vector<T>>> &v)
{
    for (int i = 0; i < (int)v.size(); i++)
    {
        os << "i = " << i << endl;
        os << v[i];
    }
    return os;
}

template <typename T>
istream &operator>>(istream &is, vector<T> &v)
{
    for (T &in : v)
        is >> in;
    return is;
}

template <typename T, typename S>
ostream &operator<<(ostream &os, map<T, S> &mp)
{
    for (auto &[key, val] : mp)
    {
        os << key << ":" << val << " ";
    }
    cout << endl;
    return os;
}

template <typename T>
ostream &operator<<(ostream &os, set<T> st)
{
    auto itr = st.begin();
    for (int i = 0; i < (int)st.size(); i++)
    {
        os << *itr << (i + 1 != (int)st.size() ? " " : "");
        itr++;
    }
    return os;
}

template <typename T>
ostream &operator<<(ostream &os, multiset<T> st)
{
    auto itr = st.begin();
    for (int i = 0; i < (int)st.size(); i++)
    {
        os << *itr << (i + 1 != (int)st.size() ? " " : "");
        itr++;
    }
    return os;
}

template <typename T>
ostream &operator<<(ostream &os, queue<T> q)
{
    while (q.size())
    {
        os << q.front() << " ";
        q.pop();
    }
    return os;
}

template <typename T>
ostream &operator<<(ostream &os, deque<T> q)
{
    while (q.size())
    {
        os << q.front() << " ";
        q.pop_front();
    }
    return os;
}

template <typename T>
ostream &operator<<(ostream &os, stack<T> st)
{
    while (st.size())
    {
        os << st.top() << " ";
        st.pop();
    }
    return os;
}

template <typename T>
ostream &operator<<(ostream &os, priority_queue<T> pq)
{
    while (pq.size())
    {
        os << pq.top() << " ";
        pq.pop();
    }
    return os;
}

template <typename T>
ostream &operator<<(ostream &os, priority_queue<T, vector<T>, greater<T>> mpq)
{
    while (mpq.size())
    {
        os << mpq.top() << " ";
        mpq.pop();
    }
    return os;
}

int main()
{
    int n, m;
    cin >> n >> m;
    vector<vector<int>> p(n, vector<int>(m));
    cin >> p;
    rep(i, n)
    {
        sort(all(p[i]));
    }
    int ok = 1e9 + 1;
    int ng = -1;
    while (abs(ok - ng) > 1)
    {
        int mid = ok + ng;
        mid /= 2;
        // debug(mid);
        vector<vector<int>> dp(n, vector<int>(m + 1));
        rep(j, m)
        {
            dp[0][j] = 1;
        }
        rep(i, n - 1)
        {
            rep(j, m)
            {
                if (dp[i][j] == 0)
                {
                    continue;
                }
                int start = lower_bound(all(p[i + 1]), p[i][j]) - p[i + 1].begin();
                int end = upper_bound(all(p[i + 1]), p[i][j] + mid) - p[i + 1].begin();
                // debug(start);
                // debug(end);
                if (start > end)
                {
                    continue;
                }
                dp[i + 1][start]++;
                dp[i + 1][end]--;
            }
            rep(j, m)
            {
                dp[i + 1][j + 1] += dp[i + 1][j];
            }
            rep(j, m)
            {
                auto chmin = [](auto &a, auto b)
                { a = min(a, b); };
                chmin(dp[i + 1][j], 1);
            }
        }
        // cout << dp << endl;
        int criteria = 0;
        rep(j, m)
        {
            criteria |= dp[n - 1][j];
        }
        // debug(criteria);
        if (criteria)
        {
            ok = mid;
        }
        else
        {
            ng = mid;
        }
    }
    if (ok == 1e9 + 1)
    {
        cout << -1 << endl;
        return 0;
    }
    cout << ok << endl;
}