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;

class Hello
{
    static void Main()
    {
        var nk = Console.ReadLine().Split().Select(int.Parse).ToArray();
        int n = nk[0], k = nk[1];

        var pair = new KeyValuePair<int, int>[n];
        for (int i = 0; i < n; i++)
        {
            var ab = Console.ReadLine().Split().Select(int.Parse).ToArray();
            int a = ab[0], b = ab[1];
            pair[i] = new KeyValuePair<int, int>(a, b);
        }
        pair = pair.OrderBy(e => e.Key).ToArray();
        long sum = 0;
        int ans = -1;
        for (int i = 0; i < n; i++)
        {
            sum += pair[i].Value;
            if (sum >= k)
            {
                ans = pair[i].Key;
                break;
            }
        }
        Console.WriteLine(ans);
    }
}