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(string[] args)
    {
        var input = Console.ReadLine().Split().Select(long.Parse).ToArray();
        long N = input[0], K = input[1];

        var bigArray = new SortedDictionary<long, long>();

        for(var i = 0; i < N; ++i)
        {
            var num_times = Console.ReadLine().Split().Select(long.Parse).ToArray();
            long num = num_times[0], times = num_times[1];
            if (!bigArray.ContainsKey(num))
                bigArray.Add(num, 0);
            bigArray[num] += times;
        }

        foreach(KeyValuePair<long, long> num_times in bigArray)
        {
            K -= num_times.Value;
            if (K > 0) continue;
            Console.WriteLine(num_times.Key);
            return;
        }
    }
}