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

int N,M,K;
int a[100000];

bool check(int x){
  int sum=K+x;

  int cnt=0;
  int h=0;
  int index=lower_bound(a,a+N,x)-a;
  if(h==index)h++;
  
  for(int i=N-1;i>=0;i--){
    if(i==index)continue;
    
    while(h<N && a[i]+a[h]<=sum){
      h++;
      if(h==index)h++;
    }

    if(h<i&&sum<a[i]+a[h]){
      cnt++;
      //      cout<<i<<' '<<h<<endl;
      h++;
    }
    
  }
  return ( cnt<M );
}

int main(){
  cin>>N>>M>>K;
  N--;
  for(int i=0;i<N;i++){
    cin>>a[i];    
  }
  sort(a,a+N);
  int left=0,right=N-1,mid;
  while(left<right){
    mid=(left+right)/2;
    if(check(mid))right=mid;
    else left=mid+1;
  }

  if( check(N-1) ==false )    cout<<-1<<endl;
  else cout<<a[left]<<endl;
  return 0;
}