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 <vector>
#include <iostream>
#include <cmath>
#include <string>
#include <cstring>
#include <algorithm>
#include <numeric>
#include <utility>
using namespace std;

int main(){
    ios::sync_with_stdio(false);
    long long int n,k;
    cin>>n>>k;
    vector<pair<long long int,long long int>>ab(n);
    for(int i=0;i<n;i++){
        cin>>ab[i].first>>ab[i].second;
    }
    sort(ab.begin(),ab.end());
    for(int i=0;;i++){
        k-=ab[i].second;
        if(k<=0){
            cout<<ab[i].first;
            break;
        }
    }
}