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;

namespace ABC061_C_Big_Array
{
	internal class Program
	{
		public static void Main(string[] args)
		{
			string[] input = Console.ReadLine().Split(' ');
			int n = int.Parse(input[0]);
			int k = int.Parse(input[1]);
			
			//解説スライドを見て書いたコード
			int[] num = new int[100000];
			for (int i = 0; i < 100000; i++)
				num[i] = 0;

			for (int i = 0; i < n; i++)
			{
				input = Console.ReadLine().Split(' ');
				int a = int.Parse(input[0]);
				int b = int.Parse(input[1]);
				num[a] += b;
			}

			int count = 0;
			for (int i = 0; i < 100000; i++)
			{
				count += num[i];
				if (count >= k)
				{
					Console.WriteLine(i);
					return;
				}
			}

			/*自分で書いたコード(TLEはともかくREになる理由がわからない)
			List<int> aList = new List<int>(n);
			List<int> bList = new List<int>(n);

			for (int i = 0; i < n; i++)
			{
				input = Console.ReadLine().Split(' ');
				aList.Add(int.Parse(input[0]));
				bList.Add(int.Parse(input[1]));
			}
			sortArr(aList, bList);

			int count = 0;
			for (int i = 0; i < n; i++)
			{
				count += bList[i];
				if (count >= k)
				{
					Console.WriteLine(aList[i]);
					return;
				}
			}*/
		}
		
		//aListを降順ソートし、それに合わせてbListもソートする
		static void sortArr(List<int> aList, List<int> bList)
		{
			for (int i = 0; i < aList.Count - 1; i++)
			{
				for (int j = i + 1; j < aList.Count; j++)
				{
					if (aList[i] > aList[j])
					{
						int value = aList[j];
						aList[j] = aList[i];
						aList[i] = value;

						value = bList[j];
						bList[j] = bList[i];
						bList[i] = value;
					}
				}
			}
		}
	}
}