#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> PII;
const int N=2e6+10;
ll n,m,k;
ll ans;
ll a[N];
bool tf[N];
vector<PII> tg;

bool check(ll mid){
    vector<PII> v;
    int i=1;
    while(i<m&&v.size()<n){
        if(a[i+1]-a[i]<=mid){
            v.push_back({i,i+1});
            i++;
        }
        i++;
    }
    if(v.size()<n) return false;
    reverse(v.begin(),v.end());
    ll cnt=0;
    for(int i=0;i<n;i++){
        if(v[i].second>tg[i].first) return false;
        if(v[i].first>tg[i].second) return false;
    }
    return true;
}

int main()
{
    cin>>n>>k;
    // int nn=2*n*;
    
    m=2*n*k;
    for(int i=m;i>0;){
        i=i-k+1;
        PII res;
        res.first=i;
        i--;
        i=i-k+1;
        res.second=i;
        i--;
        tg.push_back(res);
    }
    for(int i=1;i<=m;i++) scanf("%lld",&a[i]);
    sort(a+1,a+1+m);
    ll l=0,r=1e9;
    while(l<r){
        ll mid=l+r>>1;
        if(check(mid)) r=mid;
        else l=mid+1;
    }
    cout<<l<<endl;
}
//51423