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 REP(i,a,b) for(int (i)=(a);(i)<(int)(b);(i)++)
#define RREP(i,a,b) for(int (i)=(a);(i)>=(int)(b);(i)--)
typedef long long ll;
typedef pair<ll, ll> P;
const int MOD = 1000000007;

template<typename T> class CumulativeSum{
    public:
        vector<T> sum;

        CumulativeSum(int n);
        void add(int i, T x);
        void build();
        T get(int i);
};

template<typename T> CumulativeSum<T>::CumulativeSum(int n){
    sum = vector<T>(n + 1, 0);
}

template<typename T> void CumulativeSum<T>::add(int i, T x){
    sum[i] += x;
}

template<typename T> void CumulativeSum<T>::build(){
    for (int i = 1; i < sum.size(); i++) sum[i] += sum[i - 1];
}

template<typename T> T CumulativeSum<T>::get(int i){
    if (i < 0) return 0;
    return sum[min(i, (int)sum.size() - 1)];
}


int main(){
    ll n, k;
    cin >> n >> k;
    vector<int> a(n), b(n);

    CumulativeSum<ll> cs(n);

    REP(i,0,n){
        cin >> a[i] >> b[i];
        cs.add(i, b[i]);
    }

    cs.build();
    
    int index = 0;
    REP(i,0,n){
        if (cs.get(i) >= k){
            index = i;
            break;
        }
    }

    cout << a[index] << endl;
    
    return 0;
}