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 <vector>
#include <algorithm>
#include <map>
using namespace std;

int main(){
  vector<int> array;

  int N, K;
  cin>>N>>K;
  
  int number, pcs; 
  map<int, unsigned long int> mp;
  for(int i = 0; i < N; i++){
    cin>>number>>pcs;

    auto itr = mp.find(number);
    if(itr != mp.end()){
      mp[number] += pcs; 
    }else{
      array.push_back(number);
      mp[number] = pcs;
    }

  }

  sort(array.begin(), array.end());

  unsigned long int index = 0;
  for (int i = 0; i < array.size(); i++){
    index += mp[array[i]] ;
    if(index >= K){
      cout<<array[i]<<endl;
      break;
    }
  }

  return 0;
}