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 Kotlin (1.0.0) (judge verdict: Accepted)

import java.util.Arrays
import java.util.ArrayList

const val MOD: Long = (1e9+7).toLong()
fun Double.format(digits: Int) = String.format("%.${digits}f", this)
fun <T : Comparable<T>> Iterable<T>.argmax(): Int? = withIndex().maxBy{it.value}?.index
fun <T : Comparable<T>> Iterable<T>.argmin(): Int? = withIndex().minBy{it.value}?.index

fun main(args: Array<String>) {
    val reader = System.`in`.bufferedReader()
    val (N, k) = reader.readLine()!!.split(" ").map{it.toLong()}
    val n = N.toInt()
    val c = Array(n, {
        val (a, b) = reader.readLine()!!.split(" ").map{it.toLong()}
        Pair(a, b)
    })

    c.sortBy {it.first}

    var sum = 0L
    for (i in 0..n-1) {
        sum += c[i].second
        if (sum >= k) {
            println(c[i].first)
            return
        }
    }
}