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++ (GCC 9.2.1) (judge verdict: Accepted)

#include <iostream>
#include <map>

using namespace std;

int main(){
  long n ,k;
  long a, b;
  cin >> n  >> k;
  map<long, long> ab;
  for(int i = 0; i < n; i++) {
    cin >> a >> b;
    auto itr = ab.find(a);
    if(itr != ab.end()) {
      itr->second = itr->second + b;
    } else {
      ab.insert(make_pair(a, b));
    }
  }
  for(auto const&[key, value] : ab) {
    if(k <= value) {
      cout << key << endl;
      break;
    } else {
      k -= value;
    }
  }
  return 0;
}