Problem:
Score : 300 points

Problem Statement

There is an empty array.
The following N operations will be performed to insert integers into the array.
In the i-th operation (1≤i≤N), b_i copies of an integer a_i are inserted into the array.
Find the K-th smallest integer in the array after the N operations.
For example, the 4-th smallest integer in the array \{1,2,2,3,3,3\} is 3.

Constraints

1≤N≤10^5

1≤a_i,b_i≤10^5

1≤K≤b_1…+…b_n

All input values are integers.

Input

Input is given from Standard Input in the following format:

N K
a_1 b_1
:
a_N b_N

Output

Print the K-th smallest integer in the array after the N operations.

Sample Input 1

3 4
1 1
2 2
3 3

Sample Output 1

3

The resulting array is the same as the one in the problem statement.

Sample Input 2

10 500000
1 100000
1 100000
1 100000
1 100000
1 100000
100000 100000
100000 100000
100000 100000
100000 100000
100000 100000

Sample Output 2

1

Solution in Scala (2.11.7) (judge verdict: Accepted)

import java.util.Scanner

object Main extends App {
  val sc = new Scanner(System.in)

  val n = sc.nextInt
  val k = sc.nextLong

  val iAbl = Vector.fill(n)((sc.nextInt, sc.nextInt))

  val abl = iAbl.sorted

  val acc = comulativeSum(abl)

  val res = acc.find(_._2 >= k).get._1

  println(res)

  def comulativeSum(intVector: Vector[(Int, Int)]): Vector[(Int, Long)] ={
    intVector.foldLeft(Vector.empty[(Int, Long)]){
      case (list, (v, acc)) =>
        if(list.isEmpty) Vector((v,acc))
        else list :+ (v, list.last._2 + acc)
    }
  }
}