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: Accepted)

#include <bits/stdc++.h>
using namespace std;
using ll = long long; 
using vpii = vector<pair<int, int>>;
#define rep(i, n) for (int i = 0; i < (int)n; i++)
#define rep1(i, n) for (int i = 1; i < (int)n; i++)
ll inf = 1e9+7;

ll gcd(ll a, ll b){
  return (b != 0) ? gcd(b, a%b) : a;
}

ll lcm(ll a, ll b){
  return (a/gcd(a,b))*b;
}

int main(){
  cin.tie(0);
  ios_base::sync_with_stdio(false);
  int n; ll k;
  cin >> n >> k;
  vpii ab(n);
  rep(i, n) cin >> ab[i].first >> ab[i].second;
  sort(ab.begin(), ab.end());
  ll cnt = 0;
  rep(i, n){
    cnt += ab[i].second;
    if(cnt >= k){cout << ab[i].first << "\n"; return 0;}
  }
  return 0;
}