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<iostream>
#include<vector>

using namespace std;
#define Vi vector<int>
#define FOR(i,n) for(int i=0;i<n;i++)
#define MAX_SIZE 100001

int main(){
  long n,k;
  cin>>n>>k;
  vector<long> v(MAX_SIZE,0),tmpa(n),tmpb(n);
  FOR(i,n)
    cin>>tmpa[i]>>tmpb[i];
  FOR(i,n)
    v[tmpa[i]]+=tmpb[i];
  for(int i=1;i<MAX_SIZE;i++){
    k-=v[i];
    if(k<=0){
      cout<<i<<endl;
      break;
    }
  }
}