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<algorithm>
#include<string>
#include<functional>
#include<utility>
#include<stack>
#include<queue>
#include<cmath>
#include<list>
#include<cstdint>
#include<vector>
#include<map>
#define rep(i,rept)	for(ll i = 0; i<rept;i++)
typedef long long ll;
const ll MOD = 1e9 + 7;
using namespace std;

int main() {
	//三日目
	ll n = 0, k = 0;
	ll a = 0, b = 0;
	ll imadoko = 0, f = 0;
	map<ll, ll> ab;
	vector<ll> type;
	cin >> n >> k;
	rep(i, n) {
		cin >> a >> b;
		if (ab[a] == 0) {
			type.push_back(a);
		}
		ab[a] += b;	
	}
	sort(type.begin(), type.end());
	while (imadoko < k) {
		imadoko += ab[type[f]];
		f++;
	}
	cout << type[f-1] << endl;
	return 0;
}