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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <vector>
#include <algorithm>

struct VectorItem
{
  uint64_t value, count;
  VectorItem(uint64_t value, uint64_t count) 
    : value(value), count(count) {}
  bool operator<(const VectorItem &item) const
    { return value < item.value; }
};

int main()
{
  uint64_t N, K;
  std::cin >> N >> K;
  --K;
  
  std::vector<VectorItem> array;
  
  for (uint64_t n = 0; n < N; ++n) {
    uint64_t a, b;
    std::cin >> a >> b;
    
    array.emplace_back(a, b);
  }
  
  std::sort(array.begin(), array.end());
  
  uint64_t k = 0, ans = array[N - 1].value;
  for (uint64_t n = 0; n < N; ++n) {
    if (k <= K && K < k + array[n].count) {
      ans = array[n].value;
    }
    k += array[n].count;
  }
  std::cout << ans << std::endl;
  
  return 0;
}