#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define endl '\n'
const ll MOD = 998244353;

int main(){
    cin.tie(0)->sync_with_stdio(0);

    int n, m;
    cin >> n >> m;
    if(n == 1){
        cout << -1 << endl;
        return 0;
    }
    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 ok=[&](int x){
        vector<bool> dp(m, true);
        for(int i = 1; i < n; i++){
            vector<bool> ndp(m, false);
            int l = 0;
            for(int r = 0; r < m; r++){
                while((l < m) && ((!dp[l]) || (D[i][r] - D[i - 1][l] > x))){
                    l++;
                }
                if(l == m) break;
                int d = D[i][r] - D[i - 1][l];
                if(0 <= d && d <= x) ndp[r] = true;
            }
            swap(dp, ndp);
        }
        for(auto tf:dp){
            if(tf) return true;
        }
        return false;
    };

    int l = -1;
    int r = 1 << 30;
    while(r - l > 1){
        int mid = (l + r) / 2;
        if(ok(mid)) r = mid;
        else l = mid;
    }
    if(r == (1 << 30)) r = -1;
    cout << r << endl;
}