#line 1 "a.cpp"
#include<iostream>
#include<algorithm>
using namespace std;
#line 1 "/home/kotatsugame/library/math/extgcd.cpp"
template<typename T>
T extgcd(T a,T b,T&x,T&y)
{
	if(b==0)
	{
		x=1;
		y=0;
		return a;
	}
	T q=a/b;
	T g=extgcd(b,a-q*b,y,x);
	y-=q*x;
	return g;
}
#line 5 "a.cpp"
int N,M;
int A[5000],B[5000];
main()
{
	cin>>N>>M;
	for(int i=0;i<N;i++)cin>>A[i];
	for(int i=0;i<M;i++)cin>>B[i];
	long ans=9e18;
	for(int i=0;i<N;i++)for(int j=0;j<M;j++)if(A[i]==B[j])
	{
		long x,y;
		long g=extgcd<long>(N,M,x,y);
		if((j-i)%g!=0)continue;
		int n=N/g,m=M/g;
		int t=(j-i)/g;
		x*=t,y*=t;
		y=-y;
		{
			int l=min(x/m,-y/n);
			if(l>=0)x-=m*l,y+=n*l;
		}
		{
			int r=min(-x/m,y/n);
			if(r>=0)x+=m*r,y-=n*r;
		}
		while(x>=m)x-=m,y+=n;
		while(x<0)x+=m,y-=n;
		ans=min(ans,x*N+i);
	}
	if(ans==(long)9e18)ans=-2;
	cout<<ans+1<<endl;
}