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)

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <queue>
#include <cmath>
#include <climits>
#include <iomanip>
#include <set>
#include <map>
using namespace std;
typedef long long ll;
int main(){
  ll n,k;
  cin >> n >> k;
  vector<pair<ll,ll>> a(n);
  for(int i = 0;i < n;i++){
    ll p,q;
    cin >> p >> q;
    a[i] = make_pair(p,q);
  }
  sort(a.begin(),a.end());
  /*for(int i = 0;i < n;i++){
    cout << a[i].first << " " << a[i].second << endl;
  }*/
  ll now = 0;
  for(int i = 0;i < n;i++){
    now += a[i].second;
    if(now >= k){
      cout << a[i].first << endl;
      return 0;
    }
  }
}