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: Wrong Answer)

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

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            //[summary]C - Big Array
            var line = ReadLine();
            long n = line[0];
            long k = line[1];

            var a = new long[n];
            var b = new long[n];

            for(int i = 0; i < n; i++)
            {
                line = ReadLine();
                long ai = line[0];
                long bi = line[1];

                a[i] = ai;

                if (i == 0)
                {
                    b[i] = bi;
                }
                else
                {
                    b[i] = b[i - 1] + bi;
                }        
            }

            long ans = 0;

            for(int i = 0; i < n; i++)
            {
                if (b[i] >= k)
                {
                    ans = a[i];
                    break;
                }
            }

            Console.WriteLine(ans);
        }

        static List<long> ReadLine()
        {
            var line = Console.ReadLine();
            var array = line.Split(' ');

            return array.Select(x => long.Parse(x)).ToList();
        }
    }
}