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<bits/stdc++.h>
using namespace std;
typedef long long ll;

int main(){
    int n; ll k; cin>>n>>k;
    map<int, ll> list;
    for(int i=0; i<n; i++){
        int a; ll b; cin>>a>>b;
        if(list.count(a)) list[a]+=b;
        else list[a]=b;
    }
    ll num = 0;
    auto begin = list.begin(), end = list.end();
    int l;
    for(auto iter = begin; iter!=end; iter++){
        num += iter->second;
        l = iter->first;
        if (num >=k)break;
    }
    cout << l << endl;
}