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>
#include<map>
using namespace std;
 
int main()
{
    // get two integers separated with half-width break
    int N; long int M;
    cin >> N >> M;

    // get a string
    map<int, long int> v2c;
    for(int i = 0; i < N; ++i){
      int a,b;
      cin >> a >> b;

      v2c[a] += b;
    }
    // output
    map<int, long int> ::iterator mit = v2c.begin();
    while(mit != v2c.end() && M > 0){
      M -= mit->second;
      ++mit;
    }
    --mit;
    cout << mit->first << endl;
    return 0;
}