#include <bits/stdc++.h>
using namespace std;
#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define mp(a,b) make_pair((a),(b))
#define pb(a) push_back((a))
#define all(x) (x).begin(),(x).end()
#define uniq(x) sort(all(x)),(x).erase(unique(all(x)),end(x))
#define fi first
#define se second
#define dbg(x) cout<<#x" = "<<((x))<<endl
template<class T,class U> ostream& operator<<(ostream& o, const pair<T,U> &p){o<<"("<<p.fi<<","<<p.se<<")";return o;}
template<class T> ostream& operator<<(ostream& o, const vector<T> &v){o<<"[";for(T t:v){o<<t<<",";}o<<"]";return o;}

#define INF 2147483600

int main(){
  int n,m;
  cin>>n>>m;
  int k; cin>>k;
  vector<int> vec(n-1);
  rep(i,n-1) cin>>vec[i];

  if(n==2){cout << vec[0] << endl; return 0;}

  sort(all(vec));
  int l=0,r=n-1;
  while(r-l>1){
    int mid = (l+r)/2;

    int p = k + vec[mid];
    int il=0, ir=n-2;
    if(ir==mid) ir--;
    if(il==mid) il++;
    int cnt=0;

    while(il<ir){
      while(il<ir && vec[il]+vec[ir] <= p){
        il++; if(il==mid) il++;
      }
      if(il>=ir) break;
      else cnt++;
      ir--;
      il++;
      if(ir==mid) ir--;
      if(il==mid) il++;
    }

    if(cnt<m) r = mid;
    else l = mid;
  }

  if(r==n-1) cout << -1 << endl;
  else cout << vec[r] << endl;

  return 0;
}