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.Collections.Generic;
using System.Linq;
using System.Numerics;
using static AtCoder.Io;

namespace AtCoder
{
    class Program
    {
        static void Main()
        {
            var n = ReadNextLong();
            var k = ReadNextLong();
            var abs = new Tuple<long, long>[n];
            for (int i = 0; i < abs.Length; i++)
            {
                abs[i] = Tuple.Create(ReadNextLong(), ReadNextLong());
            }
            long count = 0;
            var ans = abs.OrderBy(x => x.Item1).SkipWhile(x => { count += x.Item2; return count < k; }).First().Item1;

            Console.WriteLine(ans);
        }
    }

    public static class Io
    {
        public static string ReadString() => Console.ReadLine();
        public static string[] ReadStringArray() => ReadString().Split(' ');
        public static int ReadInt() => int.Parse(ReadString());
        public static long ReadLong() => long.Parse(ReadString());
        public static BigInteger ReadBigInteger() => BigInteger.Parse(ReadString());
        public static int[] ReadIntArray() => ReadStringArray().ParseInt().ToArray();
        public static long[] ReadLongArray() => ReadStringArray().ParseLong().ToArray();
        public static BigInteger[] ReadBigIntegerArray() => ReadStringArray().ParseBigInteger().ToArray();
        public static IEnumerable<int> ParseInt(this IEnumerable<string> source) => source.Select(int.Parse);
        public static IEnumerable<long> ParseLong(this IEnumerable<string> source) => source.Select(long.Parse);
        public static IEnumerable<BigInteger> ParseBigInteger(this IEnumerable<string> source) => source.Select(BigInteger.Parse);

        public static string[] Buffer = new string[] { };
        public static int Index;
        public static string ReadStringNext()
        {
            if (Buffer.Length == 0 || Buffer.Length <= Index)
            {
                Buffer = ReadStringArray();
                Index = 0;
            }
            return Buffer[Index++];
        }
        public static int ReadNextInt() => int.Parse(ReadStringNext());
        public static long ReadNextLong() => long.Parse(ReadStringNext());
        public static BigInteger ReadNextBigInteger() => BigInteger.Parse(ReadStringNext());
    }
}