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

namespace C
{
    public class Program
    {
        static void Main(string[] args)
        {
            var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);
            Solve();
            Console.Out.Flush();
        }

        public static void Solve()
        {
            var NK = Console.ReadLine().Trim().Split(' ').Select(long.Parse).ToArray();
            var (N, K) = (NK[0], NK[1]);
            var dict = new Dictionary<long, long>();
            for (var i = 0; i < N; i++)
            {
                var ab = Console.ReadLine().Trim().Split(' ').Select(long.Parse).ToArray();
                var (a, b) = (ab[0], ab[1]);
                if (dict.ContainsKey(a)) dict[a] += b;
                else dict[a] = b;
            }
            var count = 0L;
            foreach (var val in dict.Keys.OrderBy(x => x).ToArray())
            {
                count += dict[val];
                if (count >= K)
                {
                    Console.WriteLine(val);
                    return;
                }
            }
        }
    }
}