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)

#pragma GCC optimize ("O3")
#pragma GCC target ("avx")

#include <bits/stdc++.h>
using namespace std;

int main() {
  int N;
  long K;
  std::cin >> N >> K;
  /*std::vector<int> a(N), b(N);
  for (long i=0; i<N; i++) {
    std::cin >> a.at(i) >> b.at(i);
  }*/
  map<int,long> m;
  for (int i=0; i<N; i++) {
    int ai, ki;
    cin >> ai >> ki;
    m[ai] += ki;
  }
  
  /*for (auto it=m.begin(); it!=m.end(); it++) {
    cerr << it->first << ' ' << it->second << endl;
  }*/
  
  long count = 0;  
  for (auto it=m.begin(); it!=m.end(); it++) {
    count += it->second;
    //cerr << it->first << endl;
    if (count>=K) {
      cout << it->first << endl;
      break;
    }
  }
  return 0;
}