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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.*;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

public class Main {

    static class Pair<K, V>{
        K key;
        V val;

        public Pair(K key, V val){
            this.key = key;
            this.val = val;
        }
    }

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

        String[] inputs = br.readLine().split(" ");
        int N = Integer.parseInt(inputs[0]);
        long K = Long.parseLong(inputs[1]);

        List<Pair<Integer, Integer>> operations = new ArrayList<>();

        for(int i = 0; i < N; i++){
            inputs = br.readLine().split(" ");
            int a = Integer.parseInt(inputs[0]);
            int b = Integer.parseInt(inputs[1]);

            Pair<Integer, Integer> operation = new Pair<>(a, b);
            operations.add(operation);
        }

        operations.sort((Comparator.comparingInt(o -> o.key)));

        long idx = 0;
        for(Pair<Integer, Integer> operation : operations){
            if(idx <= K && K <= idx + operation.val){
                bw.write(String.format("%d\n", operation.key));
                bw.flush();
                return;
            }
            idx += operation.val;
        }
    }
}