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<map>
#include<vector>
#include<algorithm>
using namespace std;

int main(){
	int N;
	long K;
	cin>>N>>K;
	map<int,long>num;
	vector<int>arr;
	int a,b;
	for(int i=0;i<N;++i){
		cin>>a>>b;
		if(num[a]==0)arr.push_back(a);
		num[a]+=b;
	}
	/*
	for(int i=0;i<arr.size();++i){
		cout<<arr[i]<<endl;
	}
	*/
	sort(arr.begin(),arr.end());
	long k=0;
	int ans;
	for(int i=0;i<N;++i){
		//cout<<k<<endl;
		if(k+num[arr[i]]>=K){
			ans=arr[i];
			break;
		}
		k+=num[arr[i]];
	}
	cout<<ans<<endl;
}