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: Runtime Error)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;

using System.IO;

class _Class
{
	void _Do()
	{
		var _s = _stringArray();
		var N_ = int.Parse(_s[0]);
		var K_ = int.Parse(_s[1]);

		var l = new Dictionary<int,int>();

	
		for (int i=0;i<N_;i++) {

			_s = _stringArray();
			int a = int.Parse(_s[0]);
			int b = int.Parse(_s[1]);

			if (l.ContainsKey(a)) {
				l[a]+= b;
			} else {
				l.Add(a,b);
			}
		}
		var k = new int[l.Count];
		var v = new int[l.Count];
		l.Keys.CopyTo(k, 0);
		l.Values.CopyTo(v, 0);
		Array.Sort(k, v);
		//
		for (int i=0;i<N_;i++) {
			if (K_<=v[i]) {
				Console.WriteLine(k[i]);
				return;
			}
			K_ -= k[i];
		} 
	}
	static void Main(string[] args)
	{
		new _Class()._Do();
	}


	// 1
	string[] _stringArray()
	{
		return Console.ReadLine().Split();
	}

	// 2.1 -2,147,483,648 ~ +2,147,483,647
	int[] _intArray()
	{
		var _s = Console.ReadLine().Split();

		var x = new int[_s.Length];
		for (var i = 0; i < _s.Length; i++)
			x[i] = int.Parse(_s[i]);

		return x;
	}

	// 2.2 -9,223,372,036,854,775,808 ~ +9,223,372,036,854,775,807
	long[] _longArray()
	{
		var _s = Console.ReadLine().Split();

		var x = new long[_s.Length];
		for (var i = 0; i < _s.Length; i++)
			x[i] = long.Parse(_s[i]);

		return x;
	}
}