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# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using static MyIO;


public class Pair
{
	public long A { get; private set; }
	public long B { get; private set; }

	public Pair(long a, long b)
	{
		A = a;
		B = b;
	}
}


public class C
{
	public static void Main()	
	{
		long N = GetLong();
		long K = GetLong();  // N <= 10^5, bi <= 10^5 thus K <= 10^10
		List<Pair> pairs = new List<Pair>();
		for(long i = 0; i < N; i++)
			pairs.Add(new Pair(GetLong(), GetLong()));
		pairs.Sort((x,y) => (int)(x.A - y.A));

		long num = 0;
		for(long i = 0; i < N; i++)
		{
			num += pairs[(int)i].B;
			if(num >= K)
			{
				Console.WriteLine(pairs[(int)i].A);
				return;
			}
		}
	}
}


public static class MyIO
{
	private static string[] args = null;
	private static int num = -1;
	private static int used = -1;

	private static string getArg()
	{
		if(used == num)
		{
			args = Console.ReadLine().Split(' ');
			num = args.Length;
			used = 0;
		}
		return args[used++];
	}

	public static int GetInt(){ return int.Parse(getArg()); }
	public static long GetLong(){ return long.Parse(getArg()); }
	public static double GetDouble(){ return double.Parse(getArg()); }
	public static string GetString(){ return getArg(); }
}