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 <string>
#include <vector>
#include <map>
#include <cmath>
#include <algorithm>
#include <functional>
#include <stack>
#include <numeric>
typedef long long ll;
using namespace std;
const int MOD = (int)1e9 + 7;
const ll INF = (ll)1e18 + 7;
#define int long long

signed main()
{
	cin.tie(0);
	ios::sync_with_stdio(false);

	int N,K;
	cin>>N>>K;
	vector<int> A(100001, 0);

	for (int i = 0; i < N; i++) {
		int a,b;
		cin>>a>>b;
		A[a] += b;
	}
	int tmp = 0;
	int ans = 0;
	for (int i = 0; i < 100001; i++) {
		tmp += A[i];
		if(tmp>=K){
			ans=i;
			break;
		}
	}
	cout << ans << endl;
	return 0;
}