#include<bits/stdc++.h>
#include<atcoder/modint>
using namespace std;
using namespace atcoder;
using ll=long long;
using mint=modint998244353;
#define rep(i,n) for(int i=0;i<n;i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
template<class T> bool chmax(T &a, T b){if (a < b){a = b;return true;} else return false;}
template<class T> bool chmin(T &a, T b){if (a > b){a = b;return true;} else return false;}

int n,m;
int main(){
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    cin>>n>>m;
    vector<vector<int>>d(n,vector<int>(m));
    rep(i,n){
        rep(j,m)cin>>d[i][j];
        sort(all(d[i]));
    }
    int ok=1<<30,ng=-1;
    while(ok-ng>1){
        int mid=(ok+ng)/2;
        vector<int>dp(m,1);
        rep(i,n-1){
            int l=0,r=0,s=0;
            bool f=true;
            vector<int>dp2(m);
            rep(j,m){
                while(r<m&&d[i+1][j]>=d[i][r]){
                    if(dp[r]==1)s++;
                    r++;
                }
                while(l<m&&d[i+1][j]>d[i][l]+mid){
                    if(dp[l]==1)s--;
                    l++;
                }
                if(s>0)dp2[j]=1;
            }
            rep(j,m)swap(dp[j],dp2[j]);
        }
        bool flag=false;
        rep(i,m)flag=flag||(dp[i]>0);
        if(flag)ok=mid;
        else ng=mid;
    }
    if(ok==1<<30)cout<<-1<<"\n";
    else cout<<ok<<"\n";
}