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: Wrong Answer)

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

using namespace std;
int main(){
    int n,k,i,y;
	long long x;
    cin >> n >> k;
    vector <pair<int, long long> > a(n);
    for(i=0;i<n;i++){
        cin >> y >> x;
        a[i] = make_pair(y,x);
    }
    sort(a.begin(),a.end());
    x = 0;
	for(i=0;i<n;i++){
        if(x<k){
        	x += a[i].second;
        }
		if(x>=k){
        	cout << a[i].first << endl;
			break;
    }
}
}