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 <bits/stdc++.h>
#define rep(i, N) for (int i = 0; i < N; i++)
using namespace std;

int main()
{
    int N, K;
    cin >> N >> K;
    vector<int> a(N), b(N);
    vector<pair<int, int> > P(N);
    rep(i, N)
    {
        cin >> a[i] >> b[i];
        P[i] = make_pair(a[i], b[i]);
    }
    sort(P.begin(), P.end());
    long long i = 0, count = 0, ans;
    while (count < K)
    {
        ans = i;
        count += P[i].second;
        i++;
    }
    cout << P[ans].first << endl;
}