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 (2.7.6) (judge verdict: Accepted)

import heapq

def solve():
  firstline = raw_input().split(' ')
  N = int(firstline[0])
  K = int(firstline[1])

  heap = []
  for i in range(N) :
    ar = raw_input().split(' ')
    a = int(ar[0])
    b = int(ar[1])
    heapq.heappush(heap, (a, b))

  count = 0
  while len(heap) > 0 :
    t = heapq.heappop(heap)
    count += t[1]
    if (count >= K) : return t[0]
  return -1

if __name__ == '__main__' :
  print solve()