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: Time Limit Exceeded)

import java.util.*;
class Main
{
    public static void main (String[] args)
    {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long k = sc.nextLong();
        int[] a = new int[n];
        long[] b = new long[n];
        Map<Integer, Long> m = new HashMap<>();
        for(int i = 0; i < n; i++){
            a[i] = sc.nextInt() - 1;
            b[i] = sc.nextLong();
            if(!m.containsKey(a[i])) m.put(a[i], (long)0);
            m.put(a[i], m.get(a[i]) + b[i]);
        }
        Arrays.sort(a);
        for(int i = 0; i < n; i++)
            b[i] = m.get(a[i]);
        int j = 0;
        long tmp = 0;
        while(tmp < k){
            if(j > 0 && a[j] == a[j-1]) continue;
            tmp += b[j];
            j++;
        }
        System.out.println(a[j-1] + 1);
    }
}