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.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CS_AtCoder {
	class Program {
		static void Main(string[] args) {
			new Calc().Solve();
		}
	}
	public class Calc {
		Scan cin = new Scan();
		public void Solve() {
			var NK = cin.ReadLong(' ');
			var list = new List<Tuple<long, long>>();
			for (int i = 0; i < NK[0]; i++) {
				var aibi = cin.ReadLong(' ');
				list.Add(new Tuple<long, long>(aibi[0], aibi[1]));
			}
			list = list.OrderBy(_ => _.Item1).ToList();
			long sum = 0;
			foreach (var item in list) {
				sum += item.Item2;
				if (sum >= NK[1]) {
					item.Item1.WL();
					return;
				}
			}
			return;
		}
	}

	public class Scan {
		public Scan() { }
		public int ReadInt() => int.Parse(Console.ReadLine());
		public int[] ReadInt(char separator) => Console.ReadLine().Split(separator).Select(int.Parse).ToArray();
		public double ReadDouble() => double.Parse(Console.ReadLine());
		public double[] ReadDouble(char separator) => Console.ReadLine().Split(separator).Select(double.Parse).ToArray();
		public long ReadLong() => long.Parse(Console.ReadLine());
		public long[] ReadLong(char separator) => Console.ReadLine().Split(separator).Select(long.Parse).ToArray();
		public string ReadLine() => Console.ReadLine();
		public string[] ReadLine(char separator) => Console.ReadLine().Split(separator).ToArray();
	}
	public static class Utils {
		public static string Docking<T>(this IEnumerable<T> collection,Func<T,string> filter = null) {
			StringBuilder sb = new StringBuilder();
			foreach (var item in collection) {
				sb.Append(filter != null ? filter(item) : item.ToString());
			}
			return sb.ToString();
		}
		public static void WL(this object obj) => Console.WriteLine(obj);
		public static int IntParse(this string s) => int.Parse(s);
		public static int IntParse(this char c) => c - '0';
	}
}