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;

class Program
{
    static void Main()
    {
        checked
        {
            var _ = Console.ReadLine().Split();
            var n = long.Parse(_[0]);
            var k = long.Parse(_[1]);

            var inss = new List<Tuple<long, long>>();

            for (var i = 0; i < n; i++)
            {
                var __ = Console.ReadLine().Split();
                var a = long.Parse(__[0]);
                var b = long.Parse(__[1]);

                inss.Add(Tuple.Create(a, b));
            }

            inss.Sort((x, y) => x.Item1.CompareTo(y.Item1));

            long cnt = 0;

            foreach (var ins in inss)
            {
                cnt += ins.Item2;

                if (cnt >= k)
                {
                    Console.WriteLine(ins.Item1);
                    return;
                }
            }

            throw new Exception();
        }
    }
}