#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i=0;i<(n);i++)
typedef long long ll;
//using mint = modint;
using mint = modint998244353;
//using mint = modint1000000007;
using P = pair<int, int>;

const ll INF=1LL<<60, dx[]={0,1,0,-1},dy[]={1,0,-1,0};
template <typename T> inline bool chmin(T& a,const T&b) {if(a>b){a=b; return 1;} return 0;}
template <typename T> inline bool chmax(T& a,const T&b) {if(a<b){a=b; return 1;} return 0;}

int main(){

    int n,m;
    cin >> n >> m;

    vector<vector<ll>> d(n,vector<ll> (m));
    rep(i,n) {
        rep(j,m) cin >> d[i][j];
        sort(d[i].begin(),d[i].end()); 
    }

    auto check=[&](long long k) -> bool {
        vector<vector<bool>> dp(n, vector<bool>(m,false));
        rep(i,m) dp[0][i]=true;

        for(int i=1;i<n;i++) {
            int t=0;
            rep(j,m) {
                if(!dp[i-1][j]) continue;
                while(t<m && d[i-1][j]>d[i][t]) t++;
                while(t<m && d[i-1][j]+k >= d[i][t]) {
                    dp[i][t]=true;
                    t++;
                }
            } 
        }

        rep(i,m) {
            if(dp[n-1][i]) return true;
        }
        return false;
    };

    ll ans=INF;
    rep(i,m){
        long long left=-1;
        long long right=2000000000;
        long long mid=(left+right)/2 +1;

        while(mid-left>1) {
            mid=(left+right)/2;
            if(check(mid)){
                right=mid;	
            } else {
                left=mid;
            }
        }
        chmin(ans,right);
    }

    cout << ((ans>1000000000)?-1:ans) << endl;

    return 0;                                                                                                      
}