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.Linq;

namespace easy_Atcoder
{
    class Program
    {
        static void Main(string[] args)
        {
            // float[] ABN = Array.ConvertAll(Console.ReadLine().Split(),float.Parse);
            int[] NK = Array.ConvertAll(Console.ReadLine().Split(),int.Parse);
            // long K = long.Parse(Console.ReadLine());
            // int[] abc = Array.ConvertAll(Console.ReadLine().Split(),int.Parse);
            // string S = Console.ReadLine();
            // int a = int.Parse(Console.ReadLine());
            // int b = int.Parse(Console.ReadLine());
            // int h = int.Parse(Console.ReadLine());
            // float N = float.Parse(Console.ReadLine());
            // string c = Console.ReadLine();
            // string B = Console.ReadLine();
            // string[] AopB = Console.ReadLine().Split();
            // var s = (new string[] { Console.ReadLine(), Console.ReadLine(), Console.ReadLine() }).Select(float.Parse);
            // float[] a = Array.ConvertAll(Console.ReadLine().Split(),float.Parse);
            // var X = Console.ReadLine();
            // int[,] abcd = new int[NMQ[2],4];
            // int[] A = new int[NMQ[0]];
            // int[] A_num = new int[NMQ[0]];
            List<Tuple<int,int>> EmpList = new List<Tuple<int,int>>();
            for(int i = 0; i<NK[0];i++){
                var read = Array.ConvertAll(Console.ReadLine().Split(),int.Parse);
                for(int j = 0; j < read[1]; j++){
                    EmpList.Add(new Tuple<int, int>(read[0],read[1]));
                }
            }
            var sortedEmpList = EmpList.OrderBy(x=>x.Item1);
            int count = 0;
            foreach(var i in sortedEmpList){
                if(count == NK[1]-1){
                    Console.WriteLine(i.Item1);
                    break;
                }
                count++;
            }
        }
        //最小公倍数
        static long Lcm(long a, long b)
        {
            return a/Gcd(a,b)*b;
        }

        //最大公約数
        static long Gcd(long m, long n)
        {
            if(n==0)return m;
            return Gcd(n,m%n);
        }
    }
}