package main

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

func configure(scanner *bufio.Scanner) {
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 1000005), 1000005)
}
func getNextString(scanner *bufio.Scanner) string {
	scanned := scanner.Scan()
	if !scanned {
		panic("scan failed")
	}
	return scanner.Text()
}
func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}
func getNextInt64(scanner *bufio.Scanner) int64 {
	i, _ := strconv.ParseInt(getNextString(scanner), 10, 64)
	return i
}
func getNextFloat64(scanner *bufio.Scanner) float64 {
	i, _ := strconv.ParseFloat(getNextString(scanner), 64)
	return i
}
func main() {
	fp := os.Stdin
	wfp := os.Stdout
	extra := 0
	if os.Getenv("I") == "IronMan" {
		fp, _ = os.Open(os.Getenv("END_GAME"))
		extra = 100
	}
	scanner := bufio.NewScanner(fp)
	configure(scanner)
	writer := bufio.NewWriter(wfp)
	defer func() {
		r := recover()
		if r != nil {
			fmt.Fprintln(writer, r)
		}
		writer.Flush()
	}()
	solve(scanner, writer)
	for i := 0; i < extra; i++ {
		fmt.Fprintln(writer, "-----------------------------------")
		solve(scanner, writer)
	}
}
func solve(scanner *bufio.Scanner, writer *bufio.Writer) {
	n := getNextInt(scanner)
	x := getNextInt(scanner)
	aa := make([]int, n)
	bb := make([]int, n)
	for i := 0; i < n; i++ {
		aa[i] = getNextInt(scanner)
	}
	for i := 0; i < n; i++ {
		bb[i] = getNextInt(scanner)
	}
	mx := n*100 + 1
	dp := makeGrid(n+1, mx)
	for i := 0; i < n+1; i++ {
		for j := 0; j < mx; j++ {
			dp[i][j] = math.MaxInt32
		}
	}
	dp[0][0] = 0
	for cur := 0; cur < n; cur++ {
		for i := n; i >= 0; i-- {
			for j := mx - 1; j >= 0; j-- {
				if dp[i][j] < math.MaxInt32 {
					dp[i][j] += bb[cur]
				}
				if i > 0 && j-aa[cur] >= 0 {
					dp[i][j] = min(dp[i][j], dp[i-1][j-aa[cur]])
				}
			}
		}
	}
	var ans int
	ans = math.MaxInt32
	for i := 1; i < n+1; i++ {
		for j := x * i; j < mx; j++ {
			ans = min(ans, dp[i][j])
		}
	}
	if ans == math.MaxInt32 {
		fmt.Fprintln(writer, -1)
		return
	}
	fmt.Fprintln(writer, ans)
}
func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}
func makeGrid(h, w int) [][]int {
	index := make([][]int, h, h)
	data := make([]int, h*w, h*w)
	for i := 0; i < h; i++ {
		index[i] = data[i*w : (i+1)*w]
	}
	return index
}