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"
using namespace std;
#define FOR(i,a,b) for(int i =(a);i<(b);i++)
#define REP(i,n) for(int i=0;i<(n);i++)
#define REPm(i,n) for(int i=(n)-1;i>=0;i--)
#define REP1(i,n) for(int i=1;i<=(n);i++)
#define mp make_pair
typedef long long ll;
int main(){
    int N,K;
    cin >> N >> K;
    vector<pair<int,int> > L;
    REP(i,N){
        int a,b;
        cin >> a >> b;
        L.push_back(mp(a,b));
    }
    sort(L.begin(),L.end());
    int index = 0;
    REP(i,N){
        index += L[i].second;
        if(index >= K){
            cout << L[i].first << endl;
            return 0;
        }
    }
    return 0;
}