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)

object Main {
  def main(args: Array[String]): Unit = {
    val Seq(n, k): Seq[Long] = io.StdIn.readLine().split(' ').map(_.toLong)

    val ops = for(_ <- 0 until n.toInt) yield {
      val Seq(a, b): Seq[Int] = io.StdIn.readLine().split(' ').map(_.toInt)
      (a, b)
    }
    val opsSorted = ops.sorted

    var acc = 0.toLong
    var ans = 0
    opsSorted.foreach{ case (a, b) =>
        acc += b
        if (k <= acc && ans == 0){
          ans = a
        }
    }
    println(ans)
  }
}