#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;
}
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