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.Linq;

class Program
{
    static void Main(string[] args) {
        int[] nk = Console.ReadLine().Split().Select(int.Parse).ToArray();
        int n = nk[0];
        int k = nk[1];
        int[][] ab = new int[n][];
        for(int i = 0; i < n; i ++) ab[i] = Console.ReadLine().Split().Select(int.Parse).ToArray();
        Console.WriteLine(solve(ab, nk[0], nk[1]));
    }
    static long solve(int[][] ab, int n, int k) {
        long ans = 0;
        if(ab.Length > 1) Array.Sort(ab, (x,y) => x[0]-y[0]);
        long count = 0;
        for(int i = 0; i < n; i ++) {
            count += ab[i][1];
            if(count >= k) {
                ans = ab[i][0];
                break;
            }
        }
        return ans;
    }
}