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 (1.6) (judge verdict: Accepted)

package main

import (
	"fmt"
	"sort"
)

func main() {
	var n, k int
	fmt.Scan(&n, &k)

	var a, b int
	m := make(map[int]int)
	for i := 0; i < n; i++ {
		fmt.Scan(&a, &b)
		m[a] += b
	}

	keys := make([]int, len(m))
	i := 0
	for key := range m {
		keys[i] = key
		i++
	}
	sort.Ints(keys)

	sum := 0
	for _, v := range keys {
		sum += m[v]
		if k <= sum {
			fmt.Println(v)
			return
		}
	}
}