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 <algorithm>
#include <vector>
#define ll long long int
using namespace std;

struct b_array {
  int num;
  int times;
  b_array(int a, int b):num(a),times(b){}
};

int N,K;
vector<b_array> b_arrays;
//vector<pair<int ,int>> inps;

int main(){
  int a,b;
  
  cin >> N >> K;
  
  for(int i=0;i<N;i++){
    cin >> a >> b;
    b_arrays.emplace_back(a,b);
  }
  sort(b_arrays.begin(),b_arrays.end(),
       [](const b_array& x, const b_array& y){return x.num<y.num;});

  for(b_array sample : b_arrays){
    K-=sample.times;
    if(K<=0) {
      cout << sample.num << endl;
      break;
    }
  }
  
  return 0;
  
}