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;
signed main(){
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  long n,a,b,k,ind=0;cin>>n>>k;
  map<int,long> m;
  for(int i=0;i<n;i++){
    cin>>a>>b;
    m[a]+=b;
  }
  if(k==1){cout<<(*m.begin()).first;}
  for(auto it=m.begin();it!=m.end();it++){
    ind+=(*it).second;
    if(ind>=k){cout<<(*it).first;return 0;}
  }
}