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(unsigned long long i=0;i<n;i++)
#define ll unsigned long long
using namespace std;
int main(){
    unsigned long long N,K;
    cin>>N>>K;
    vector<unsigned long long> mo;
    map<unsigned long long,unsigned long long> ko;
    REP(i,N){
        unsigned long long a,b;cin>>a>>b;
        auto in = ko.find(a);
        if(in != ko.end()){
            in->second+=b;
        } else {
            ko.insert(make_pair(a,b));
            mo.push_back(a);
        }
    }
    sort(mo.begin(),mo.end());
    REP(i,mo.size()){
        if(K-ko[mo[i]]<=0){
            cout<<mo[i]<<endl;
            return 0;
        } else {
            K-=ko[mo[i]];
        }
    }
}