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;

namespace CSharpSample01
{

    class Program
    {

        static void Main(string[] args)
        {
            string[] input = Console.ReadLine().Split(' ');
            int N = int.Parse(input[0]);
            long K = long.Parse(input[1]);

            Dictionary<int, long> dic = new Dictionary<int, long>();          

            for (int i = 0; i < N; i++)
            {
                input = Console.ReadLine().Split(' ');
                int a = int.Parse(input[0]);
                long b = long.Parse(input[1]);

                if (!dic.ContainsKey(a))
                {
                    dic[a] = b;
                }
                else
                {
                    dic[a] += b;
                }

            }

            var dic_sort = dic.OrderBy(x => x.Key);

            long cnt = 0;
            int ans = -1;

            foreach (var s in dic_sort)
            {

                int val = s.Key;
                long num = s.Value;

                if (cnt + num < K)
                {
                    cnt += num;
                }
                else
                {
                    ans = val;
                    break;
                }

            }

            Console.WriteLine(ans);

        }
    }
}