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++ (GCC 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); i++)
#define irep(i, n) for (int i = (n); i >= 0; i++)
using namespace std;
using ll = long long;
using P = pair<int, int>;
const int INF = 1 << 30;
 
int main() {
  ll n,k;
  cin >> n >> k;
  map<int,ll> x; 
  rep(i,n) {
    int a,b;
    cin >> a >> b;
    x[a] += b;
  }
  vector<pair<int,ll>> y;
  rep(i,100001) {
    if (x[i] > 0) y.push_back(make_pair(i,x[i]));
  }
  sort(y.begin(), y.end());
  ll cnt = 0;
  for (auto v: y) {
    if (cnt + v.second >= k) {cout << v.first << endl; break;}
    cnt += v.second;
  }
  return 0;
}