#include<bits/stdc++.h>
using namespace std;

int globalMaximum=0;

void calculate_globalMaximum(int i,vector<int>&v,vector<int>&arr,int m){

   if(v.size()==m){
        int currentMinimum=1e9;
        for(int j=1;j<m;j++){
            currentMinimum=min(currentMinimum,v[j]-v[j-1]);
        }
        globalMaximum=max(currentMinimum,globalMaximum);
        return;
    }

    if(i==arr.size())return;
    v.push_back(arr[i]);
    calculate_globalMaximum(i+1,v,arr,m);
    v.pop_back();
    calculate_globalMaximum(i+1,v,arr,m);
}

int main()
{
   int n;
   cin>>n;
   vector<int>arr(n);
   for(int i=0;i<n;i++){
    cin>>arr[i];
   }
   int m;
   cin>>m;
   vector<int>v;
   calculate_globalMaximum(0,v,arr,m);
   cout<<globalMaximum<<endl;

   return 0;
}