import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    long m = sc.nextLong();
    long A = sc.nextLong();
    long[] a = new long[n - 1];
    for(int i = 0; i < n - 1; i++) {
      a[i] = sc.nextLong();
    }
    Arrays.sort(a);
    long l = 0;
    long r = n - 1;
    long ans = -1;
    while(l < r) {
      long med = (l + r) / 2;
      long t = A + a[(int)med];
      long p = 0;
      int left = 0;
      int right = n - 2;
      while(left < right) {
        if(left == (int)med) {
          left++;
        } else if(right == (int)med) {
          right--;
        } else {
          long s = a[left] + a[right];
          if(s > t) {
            p++;
            right--;
            left++;
          } else {
            left++;
          }
        }
      }
      if(p >= m) {
        l = med + 1;
      } else {
        ans = a[(int)med];
        r = med;
      }
    }
    System.out.println(ans);
  }
}