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;

namespace AtCorderPractice
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            var _ = LnInts();
            var N = _[0]; var K = _[1];
            var abz = new List<long[]>();
            for (var i = 0; i < N; i++)
            {
                var ab = LnLngs();
                abz.Add(ab);
            }
            abz.Sort((a, b) => (int)a[0] - (int)b[0]);
            var cursor = 0L;
            var result = 0L;
            for (int i = 0; i < abz.Count; i++)
            {
                cursor += abz[i][1];
                if (cursor >= K) { result = abz[i][0]; break; }
            }
            Console.WriteLine(result);
        }

        public static string[] LnStrs()
        {
            var vs = Console.ReadLine().Trim().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
            return vs;
        }
        public static string LnStr()
        {
            var vs = Console.ReadLine().Trim();
            return vs;
        }
        public static int[] LnInts()
        {
            var vs = Console.ReadLine().Trim().Split(new[] {' '},StringSplitOptions.RemoveEmptyEntries);
            var ins = new int[vs.Length];
            for (int i = 0; i < vs.Length; i++) ins[i] = int.Parse(vs[i]);
            return ins;
        }
        public static long[] LnLngs()
        {
            var vs = Console.ReadLine().Trim().Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
            var ins = new long[vs.Length];
            for (int i = 0; i < vs.Length; i++) ins[i] = long.Parse(vs[i]);
            return ins;
        }
        public static int LnInt()
        {
            var vs = Console.ReadLine().Trim();
            return int.Parse(vs);
        }
    }
}