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 scala.io.StdIn._
object Main extends App {
  val Array(n, k) = readLine.trim.split(' ').map(_.toLong)
  val operations = Array.tabulate(n.toInt){_ ⇒
    val Array(a, b) = readLine.trim.split(' ').map(_.toInt)
    (a, b)
  }.sortBy(_._1)
  val count = operations.map(_._2.toLong)
  for (i ← count.indices.tail) count(i) += count(i - 1)
  println(operations(lowerBound(count, k))._1)
  def lowerBound(array: Array[Long], target: Long): Int = {
    var left = 0
    var right = array.length
    while(left < right) {
      val mid = (left + right) / 2
      if (array(mid) < target) left = mid + 1
      else right = mid
    }
    right
  }
}