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

int main(){
  int N, K;
  cin >> N >> K;
  vector<int> a(N);
  vector<int> b(N);
  vector<int> dp(N);
  for(int i=0; i<N; i++) cin >> a.at(i) >> b.at(i);
  int ans;
  dp.at(0)=b.at(0);
  for(int i=1; i<N; i++){
    dp.at(i)=dp.at(i-1)+b.at(i);
    if(K<=dp.at(i)){
      ans=a.at(i);
      break;
    }
  }
  cout << ans << endl;
}