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;

namespace CSharpSample01
{

    class ValNum
    {
        public int val;
        public long num;
    }
    
    
    class Program
    {

        static int Lower_Bound(List<ValNum> valnum, int next_ind, int K)
        {
            int left = -1;  //条件を満たさない
            int right = next_ind;  //条件を満たす

            while(Math.Abs(right - left) > 1)
            {
                int mid = (left + right) / 2;

                if(valnum[mid].num >= K)
                {
                    right = mid;
                }
                else
                {
                    left = mid;
                }

            }

            return valnum[right].val;
        }

        static void Main(string[] args)
        {
            string[] input = Console.ReadLine().Split(' ');
            int N = int.Parse(input[0]);
            int K = int.Parse(input[1]);
            List<ValNum> valnum = new List<ValNum>();
            //dic[val] := 配列に入っている値valの個数
            Dictionary<int, int> dic = new Dictionary<int, int>();

            int next_ind = 0;
            for(int i = 0; i < N; i++)
            {
                input = Console.ReadLine().Split(' ');
                int a = int.Parse(input[0]);
                int b = int.Parse(input[1]);
                if (dic.ContainsKey(a))
                {
                    valnum[dic[a]].num += b;
                }
                else
                {
                    dic[a] = next_ind;
                    valnum.Add(new ValNum() { val = a, num = b });
                    next_ind++;
                }
            }

           
            valnum = valnum.OrderBy(x => x.val).ToList();

            for(int i = 1; i < next_ind; i++)
            {
                valnum[i].num += valnum[i - 1].num;
            }           

            Console.WriteLine(Lower_Bound(valnum, next_ind, K));
            

        }
    }
}