#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#ifdef LOCAL
#include "algo/debug.h"
#else
#define debug(...) (void(0))
#endif
void run_case();
int main() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);
    int T = 1;
    // cin >> T;
    while (T--) run_case();
    return 0;
}
void run_case() {
    int N, M;
    cin >> N >> M;
    vector<vector<int>> D(N, vector<int>(M));
    for(int i = 0; i < N; i++) {
        for(int j = 0; j < M; j++) cin >> D[i][j];
        sort(D[i].begin(), D[i].end());
    }
    auto Check = [&](ll x) -> bool {
        vector<int> dp(M, 1);
        for(int it = 1; it < N; it++) {
            vector<int> ndp(M, 0);
            vector<int> pref(M + 1);
            for(int j = 0; j < M; j++) pref[j + 1] = pref[j] + dp[j];
            int l = 0, r = 0;
            for(int j = 0; j < M; j++) {
                while(l < M && D[it - 1][l] < D[it][j] - x) l++;
                while(r < M && D[it - 1][r] <= D[it][j]) r++;
                ndp[j] = (pref[r] - pref[l]) > 0;
            }
            swap(dp, ndp);
        }
        bool ok = false;
        for(int j = 0; j < M; j++) if(dp[j]) ok = true;
        return ok;
    };

    if(Check(0)) {
        cout << 0 << endl;
    } else {
        ll ok = 1e10, ng = 0;
        while(ok - ng > 1) {
            ll mi = (ok + ng) / 2;
            (Check(mi) ? ok : ng) = mi;
        }
        cout << (ok == (ll)1e10? -1 : ok) << endl;
    }
}