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 <iostream>
#include<algorithm>
#include<cmath>
#include<vector>
using namespace std;
typedef long long ll;
#define rep(i,n) for(int i = 0; i < n;i++)
int main(void) {
    ll a[100001], n, k, x, y, sum = 0;
    cin >> n >> k;
    rep(i, n) {
        cin >> x >> y;
        a[x] += y;
    }
    for (int i = 1; i <= 10000000000;i++) {
        sum += a[i];
        if (a[i] >= k) {
            cout << i << endl;
            break;
        }
        k -= a[i];
    }
}