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++ (GCC 9.2.1) (judge verdict: Accepted)

#include <iostream>
#include <map>
using namespace std;
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    long long N,K;
    cin >> N >> K;
    map<int, long long> mp;
    for(int i = 0; i < N; ++i){
        int a, b; cin >> a >> b;
        mp[a] += b;
    }
    
    for(auto it = mp.begin(); it != mp.end(); ++it){
        if(K - it->second <= 0){
            cout << it->first << endl;
            break;
        }
        K -= it->second;
    }
    return 0;
}