#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000001

int main(){
	
	int N,M;
	cin>>N>>M;
	
	vector<int> A(N),B(M);
	rep(i,N)cin>>A[i];
	rep(i,M)cin>>B[i];
	int g = gcd(N,M);
	int ans = Inf;
	rep(i,N){
		rep(j,M){
			if(A[i]==B[j]){
				auto ret = crt({i,j},{N,M});
				if(ret.second==0)continue;
				ans = min(ans,(int)ret.first);
			}
		}
	}
	if(ans==Inf)ans = -1;
	else ans++;
	
	cout<<ans<<endl;
	
	return 0;
}