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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.util.Map;
import java.util.Map.Entry;
import java.util.Scanner;
import java.util.TreeMap;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long k = sc.nextLong();
        Map<Integer,Long> map = new TreeMap<>();
        for(int i = 0; i < n; i++) {
            int key = sc.nextInt();
            long value = sc.nextInt();
            if(map.containsKey(key)) {
                map.put(key, map.get(key) + value);
            }else {
                map.put(key, value);
            }
        }
        long sum = 0l;
        for(Entry<Integer, Long> entry : map.entrySet()) {
            sum += entry.getValue();
            if(sum >= k) {
                System.out.println(entry.getKey());
                return;
            }
        }
    }
}