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 Go (1.6) (judge verdict: Accepted)

package main
import . "fmt"
import "sort"
func main() {
  var n,a,b,i int
  var k int64
  var keys []int
  m := map[int]int64{}
  Scan(&n,&k)
  for i=0;i<n;i++ {
    Scan(&a,&b)
    if v,ok := m[a];ok {
      m[a] = v+int64(b)
    } else {
      m[a] = int64(b)
    }
  }
  n = len(m)
  keys = make([]int,n)
  i = 0
  for key,_ := range m {
    keys[i] = key
    i++
  }
  sort.Ints(keys)
  for i=0;i<n;i++ {
    v := m[keys[i]]
    if k <= v {
      Println(keys[i])
      break
    }
    k -= v
  }
}