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 rp(i,n) for(int i=0;i<n;i++)
#define rep(i,m,n) for(int i=m;i<=n;i++)
#define lrp(i,n) for(long long i=0;i<n;i++)
#define lrep(i,m,n) for(long long i=m;i<=n;i++)
#define sort(a) sort(a.begin(),a.end())
#define reverse(a) reverse(a.begin(),a.end())
#define pb push_back
#define elif else if
#define unique(a) a.erase(unique(a.begin(),a.end()),a.end())
typedef vector<int> vi;
typedef vector<long long> vl;
typedef vector<string> vs;
typedef vector<char> vc;
typedef long long ll;
typedef string S;
typedef queue<int> qi;

int main(){
    int n,k;
    cin >> n >> k;
    vl s(n);
    vector<pair<ll,ll>> a(n);
    rp(i,n){
        cin >> a.at(i).first >> a.at(i).second;
    }
    sort(a);
    s.at(0)=a.at(0).second;
    if(s.at(0)>=k){
        cout << a.at(0).first << endl;
        return 0;
    }
    rep(i,1,n-1){
        s.at(i)=s.at(i-1)+a.at(i).second;
        if(s.at(i)>=k){
            cout << a.at(i).first << endl;
            return 0;
        }
    }
    
    return 0;
}