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 Go (1.14.1) (judge verdict: Accepted)

package main

import (
	"fmt"
	"sort"
)

type S struct {
	k, v int
}

func main() {
	var N, K int
	fmt.Scan(&N, &K)
	D := make(map[int]int)
	for i := 0; i < N; i++ {
		var a, b int
		fmt.Scan(&a, &b)
		D[a] += b
	}
	Ss := make([]S, len(D))
	idx := 0
	for k, v := range D {
		Ss[idx] = S{k: k, v: v}
		idx++
	}
	sort.Slice(Ss, func(i, j int) bool { return Ss[i].k < Ss[j].k })
	for i := 1; i < len(Ss); i++ {
		Ss[i].v += Ss[i-1].v
	}
	for _, s := range Ss {
		if K <= s.v {
			fmt.Println(s.k)
			return
		}
	}
	panic("あわわあわわわ、わぁ")
}