#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
    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());
    }
    int l = -1, r = 2e9;
    while(r-l > 1){
        int lim = (l+r)/2;
        bool ok = false;
        vector<vector<bool>> dp(N,vector<bool>(M,false));
        for(int i=0;i<M;i++) dp[0][i] = true;
        for(int i=1;i<N;i++){
            int ind_l = 0, ind_r = 0, count = 0;
            for(int j=0;j<M;j++){
                while(ind_l < M && D[i-1][ind_l] < D[i][j]-lim){
                    if(dp[i-1][ind_l]) count--;
                    ind_l++;
                }
                while(ind_r < M && D[i-1][ind_r] <= D[i][j]){
                    if(dp[i-1][ind_r]) count++;
                    ind_r++;
                }
                dp[i][j] = (count > 0);
            }
        }
        for(int i=0;i<M;i++)if(dp[N-1][i]) ok = true;
        if(ok) r = lim;
        else l = lim;
    }
    if(r == 2e9){
        cout<<-1<<endl;
        return 0;
    }
    cout<<r<<endl;
}