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 io.StdIn.readLine
import annotation.tailrec

object Main extends App {
  val (n, k) = readLine.split(" ") match {
    case Array(n, k) => (n.toInt, k.toLong)
  }
  val abs = List.fill(n)(readLine.split(" ").map(_.toInt) match {
    case Array(a, b) => (a, b)
  }).sortBy(_._1)

  println(solve(k, abs))

  @tailrec def solve(k: Long, abs: List[(Int, Int)]): Int = {
    val (a, b) = abs.head
    if (k <= b) a else solve(k - b, abs.tail)
  }
}