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 <bits/stdc++.h>

using namespace std;
typedef long long ll;

#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); ++i)
#define all(a) (a).begin(), (a).end()
#define all2(a, b) (a).begin(), (a).begin() + (b)
#define debug(vari) cerr << #vari << " = " << (vari) << endl;

// bool isOk(int index, int key)
// {
//     if (d[index] >= key)
//         return true;
//     else
//         return false;
// }

// int C(int key)
// {
//     int ng = -1;
//     int ok = N;

//     while (abs(ok - ng) > 1)
//     {
//         int mid = (ok + ng) / 2;
//         if (isOk(mid, key))
//             ok = mid;
//         else
//             ng = mid;
//     }
//     return ok;
// }

int main()
{
    ll N, K;
    cin >> N >> K;
    vector<pair<int, int>> p(N);
    rep(i, N) cin >> p[i].first >> p[i].second;
    sort(all(p));

    ll cnt = 0;
    rep(i, N)
    {
        cnt += p[i].second;
        if (K <= cnt)
        {
            cout << p[i].first << endl;
            return 0;
        }
    }
    return 0;
}