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 <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <map>
#include <memory>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <sstream>
#include <unordered_map>
#include <vector>


#define INF 4000000000000000000LL
#define MOD 1000000007
#define ALL(x) std::begin(x), std::end(x)


int main(int argc, char** argv)
{
  std::cin.tie(0);
  std::ios_base::sync_with_stdio(0);

  std::cout << std::fixed << std::setprecision(6);
  std::cerr << std::fixed << std::setprecision(6);

  int N, a, b;

  long long K;

  std::cin >> N >> K;

  std::map<int, long> map;

  for (int i = 0; i < N; i ++) {
    std::cin >> a >> b;

    map[a] += b;
  }

  for (const auto& kv : map) {
    if (K <= kv.second) {
      std::cout << kv.first << ' ' << std::endl;

      break;
    }

    K -= kv.second;
  }

  return 0;
}