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: Wrong Answer)

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <utility>
using namespace std;

int main() {
  int n, k;
  cin >> n >> k;

  vector<pair<int, int>> c;
  c.reserve(n);
  for (int i = 0; i < n; ++i) {
    int a, b;
    cin >> a >> b;

    c.emplace_back(make_pair(a, b));
  }
  sort(c.begin(), c.end());
  
  for (int i = 0; i < n; ++i) {
    const auto &t = c[i];
    if (t.second >= k) {
      cout << t.first << endl;
      break;
    } else {
      k -= t.second;
    }
  }
  return 0;
}