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;

class program
{
    static void Main(string[] args)
    {
        /*
         * 方針：
         * (ai,bi)を(index,value)とみて、クエリが来るたびにsum[index]+=value;とする。
         * 全部読み取ったらindex=0からforLoopでK-sum[index]を計算、K<=0となったらその時のindexが答え。
         */
        string[] inputs = Console.ReadLine().Split();
        long N = long.Parse(inputs[0]);
        long K = long.Parse(inputs[1]);

        long[] sum = new long[100001];

        for(int i = 0; i < N; i++)
        {
            inputs = Console.ReadLine().Split();
            long index = long.Parse(inputs[0]);
            long value = long.Parse(inputs[1]);
            sum[index] += value;
        }
        for(int i=1;i< 100001; i++)
        {
            K -= sum[i];
            if (K <= 0)
            {
                Console.WriteLine(i);
                break;
            }
        }

    }
}