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: Runtime Error)

package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"sort"
	"strconv"
)

func main() {
	N := nextInt()
	K := nextInt()
	var list []int
	for i := 0; i < N; i++ {
		a := nextInt()
		b := nextInt()
		for j := 0; j < b; j++ {
			list = append(list, a)
		}
	}

	sort.Ints(list)
	fmt.Println(list[K-1])
}

// Input. ----------

var sc = bufio.NewScanner(os.Stdin)

func init() {
	sc.Buffer([]byte{}, math.MaxInt64)
	sc.Split(bufio.ScanWords)
}

func nextInt() int {
	sc.Scan()
	i, err := strconv.Atoi(sc.Text())
	if err != nil {
		panic(err)
	}

	return i
}

func nextString() string {
	sc.Scan()
	if err := sc.Err(); err != nil {
		panic(err)
	}

	return sc.Text()
}

// ---------- Input.

// Util. ----------

func min(x, y int) int {
	return int(math.Min(float64(x), float64(y)))
}

func max(x, y int) int {
	return int(math.Max(float64(x), float64(y)))
}

// ---------- Util.