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 Python (3.4.3) (judge verdict: Accepted)

# -*- coding: utf-8 -*-
import math

if __name__ == '__main__':
    N, K = map(int, input().split())
    A, B = [], []
    for i in range(N):
        a, b = map(int, input().split())
        A.append(a)
        B.append(b)

    z = zip(A, B)
    z = sorted(z)

    A, B = zip(*z)

    val = 0
    for i in range(len(A)):
        val += B[i]
        if val >= K:
            print(A[i])
            exit()