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.Linq;
using System.Collections.Generic;
 
class MainClass {
  public static void Main (string[] args) {
    var list = Console.ReadLine().Split(' ').Select(long.Parse).ToArray();
    var N = list[0];
    var K = list[1];
 
    var dic = new Dictionary<long, long>();
 
    for(var i = 0; i < N; i++){
      var temp = Console.ReadLine().Split(' ').Select(long.Parse);
      if(dic.ContainsKey(temp.ElementAt(0))){
        dic[temp.ElementAt(0)] += temp.ElementAt(1);
      }else{
        dic.Add(temp.ElementAt(0), temp.ElementAt(1));
      }
     
    }
    var a = dic.Select(x => x).OrderBy(x => x.Key).ToList();
    var sum = (long)0;
    for(var i = 0; i < N; i++){
        sum += a[i].Value;
        if(sum >= K){
          Console.WriteLine(a[i].Key);
          return;
        }
    }
 
  }
}