package main

import . "fmt"
import . "os"
import bf "bufio"

func main() {
	rd:=bf.NewReader(Stdin)
	var n,t int
	Fscan(rd,&n,&t)
	ts:=make([]int,n-1)
	for i:=range ts {
		Fscan(rd,&ts[i])
	}
	var k int
	Fscan(rd,&k)
	xs:=make([]int,k)
	for i:=range xs {
		Fscan(rd,&xs[i])
	}
	var ans int
	for i,e:=range ts {
		t-=e
		for len(xs)>0&&t<=0&&xs[0]<=i+1 {
			ans++
			t+=10
			xs=xs[1:]
		}
		if t<=0 {
			Println(-1)
			return
		}
	}
	Println(ans)
}