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 <vector>
#include <utility>
#include <algorithm>

using namespace std;

int N = 0;
long long int K = 0;
vector< pair<int,int> > p;

int main(void){
    int a = 0, b = 0;

    cin >> N >> K;
    p.resize(N);
    for(int i=0; i<N; ++i){
        cin >> p[i].first >> p[i].second;
    }

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

    int res = 0;
    for(int i=0; i<N; ++i){
        K -= p[i].second;
        if(K <= 0){
            res = p[i].first;
            break;
        }
    }

    cout << res << endl;
}