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>
std::map<int, int> m;
int n, k, a, b;
std::vector<std::pair<int, long long>> vec;

int main() {
    std::cin >> n >> k;
    for (int i = 0; i < n; i++) {
        std::cin >> a >> b;
        m[a] += b;
    }
    
    for (auto e: m) {
        vec.push_back(e);
    }
    std::sort(vec.begin(), vec.end());
    long long sum = 0;
    for (int i = 0; i < vec.size(); i++) {
        sum += vec[i].second;
        if (k <= sum) {
            std::cout << vec[i].first << std::endl;
            return 0;
        }
    }
}