#include <atcoder/all>
using namespace atcoder;
#include <bits/stdc++.h>
using namespace std;
// #include <boost/multiprecision/cpp_int.hpp>
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i,a,b) for (int i = (int)(a); i < (int)(b); i++)
#define all(v) v.begin(),v.end()
#define inc(x,l,r) ((l)<=(x)&&(x)<(r)) 
#define Unique(x) sort(all(x)), x.erase(unique(all(x)), x.end())
typedef long long ll;
#define int ll
using ld = long double;
using vi = vector<int>;
using vs = vector<string>;
using P = pair<int,int>;
using vp = vector<P>;
// using Bint = boost::multiprecision::cpp_int;
template<typename T> using priority_queue_greater = priority_queue<T, vector<T>, greater<T>>;
template<typename T> ostream &operator<<(ostream &os,const vector<T> &v){rep(i,v.size())os<<v[i]<<(i+1!=v.size()?" ":"");return os;}
template<typename T> istream &operator>>(istream& is,vector<T> &v){for(T &in:v)is>>in;return is;}
template<class... T> void _IN(T&... a){(cin>> ... >> a);}
template<class T> void _OUT(T& a){cout <<a<< '\n';}
template<class T,class... Ts> void _OUT(const T&a, const Ts&... b){cout<< a;(cout<<...<<(cout<<' ',b));cout<<'\n';}
#define INT(...) int __VA_ARGS__; _IN(__VA_ARGS__)
#define STR(...) string __VA_ARGS__; _IN(__VA_ARGS__)
#define pcnt __builtin_popcountll
int sign(int x){return (x>0)-(x<0);}
int ceil(int x,int y){assert(y!=0);if(sign(x)==sign(y))return (x+y-1)/y;return -((-x/y));}
int floor(int x,int y){assert(y!=0);if(sign(x)==sign(y))return x/y;if(y<0)x*=-1,y*=-1;return x/y-(x%y<0);}
int abs(int x,int y){return abs(x-y);}
bool ins(string s,string t){return s.find(t)!=string::npos;}
P operator+ (const P &p, const P &q){ return P{p.first+q.first,p.second+q.second};}
P operator- (const P &p, const P &q){ return P{p.first-q.first,p.second-q.second};}
template<typename T1,typename T2> ostream &operator<< (ostream &os, const pair<T1,T2> &p){os << p.first <<" "<<p.second;return os;}
ostream &operator<< (ostream &os, const modint1000000007 &m){os << m.val();return os;}
istream &operator>> (istream &is, modint1000000007 &m){ll in;is>>in;m=in;return is;}
ostream &operator<< (ostream &os, const modint998244353 &m){os << m.val();return os;}
istream &operator>> (istream &is, modint998244353 &m){ll in;is>>in;m=in;return is;}
template<typename T1,typename T2> bool chmax(T1 &a, const T2 b) {if (a < b) {a = b; return true;} else return false; }
template<typename T1,typename T2> bool chmin(T1 &a, const T2 b) {if (a > b) {a = b; return true;} else return false; }
void yesno(bool ok,string y="Yes",string n="No"){ cout<<(ok?y:n)<<endl;}
int di[]={-1,0,1,0,-1,-1,1,1};
int dj[]={0,1,0,-1,-1,1,-1,1};
const int INF = 8e18;
//using mint = modint1000000007;
//using mint = modint998244353;

signed main() {
    cin.tie(0);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);

    INT(n,m);
    vector D(n,vi(m));cin>>D;
    rep(i,n)sort(all(D[i]));
    int ok = 1e9+10;
    int ng = -1;

    auto f = [&](int x){
        //x以下は遷移できる
        vector dp(n,vi(m));
        rep(j,m){
            auto nj = upper_bound(all(D[0]),D[1][j])-D[0].begin()-1;
            if(nj>=0 && D[1][j]-D[0][nj]<=x)dp[1][j] = 1;
        }
        for(int i=1;i<n-1;i++){
            rep(j,m-1)dp[i][j+1]+=dp[i][j];
            auto sum = [&](int l,int r){
                if(r<=l)return 0ll;
                int res = dp[i][r-1];
                if(l)res -= dp[i][l-1];
                return res;
            };
            rep(j,m){
                int l = lower_bound(all(D[i]),D[i+1][j]-x)-D[i].begin();
                int r = upper_bound(all(D[i]),D[i+1][j])-D[i].begin();
                if(sum(l,r))dp[i+1][j] = 1;
            }
        }
        rep(j,m)if(dp[n-1][j])return true;
        return false;
    };
    while(abs(ng-ok)>1){
        int mid = ng+(ok-ng)/2;
        if(f(mid))ok=mid;
        else ng = mid;
    }

    if(ok==1e9+10)ok=-1;
    cout << ok << endl;
    return 0;
}