package main

import . "fmt"

func main() {
	var n,m int
	Scan(&n,&m)
	a:=make([]int,n*m)
	b:=make([]int,n*m)
	for i:=range a[:n] {
		Scan(&a[i])
		for k:=i+n;k<len(a);k+=n {
			a[k]=a[i] 
		}
	}
	for i:=range b[:m] {
		Scan(&b[i])
		for k:=i+m;k<len(b);k+=m {
			b[k]=b[i]
		}
	}
	for i, v:=range a {
		if v==b[i] {
			Println(i+1)
			return
		}
	}
	Println(-1)
}