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 C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;

class MainClass
{
    static void Main()
    {
        var NK = Console.ReadLine().Split().Select(long.Parse).ToArray();
        int N = (int)NK[0];long K = NK[1];
        var ab = new long[N][];
        for (int i = 0; i < N; i++)
        {
            ab[i] = Console.ReadLine().Split().Select(long.Parse).ToArray();
        }
        Array.Sort(ab, (x, y) => x[0].CompareTo(y[0]));

        long index = 0;
        int num = -1;
        for(int i = 0; i < ab.Length; i++)
        {
            num = (int)ab[i][0];
            index += ab[i][1];

            if (index >= K) break;
        }
        Console.WriteLine(num);
    }
}