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 <algorithm>
using namespace std;

struct Node
{
	int a, b;
};
bool cmp(Node &n1, Node &n2)
{
	return n1.a < n2.a;
}

int main()
{
	int N;
	long long K;
	cin >> N >> K;
	vector<Node> vec(N);

	for (int i = 0; i < N; ++i)
	{
		cin >> vec[i].a >> vec[i].b;	
	}
	sort(vec.begin(), vec.end(), cmp);
	for (int i = 0; i < N; ++i)
	{
		if (K > vec[i].b)
		{
			K -= vec[i].b;
		}
		else {
			cout << vec[i].a << endl;
			break;
		}
	}
	return 0;
}