#include <atcoder/math>
#include <iostream>
#include <stdio.h>
#include <vector>
#include <utility>
//#include <algorithm>
using namespace std;
using namespace atcoder;
#define ull  unsigned long long
#define ll long long
#define Pll pair<long,long>
#define INF 1000000000000000000

ull min(ull x,ull y){
  if(x>y)return y;
  return x;
}

ll gcd(ll x,ll y){
  if(x%y)return gcd(y,x%y);
  return y;
}

ll lcm(ll x,ll y){
  return x/gcd(x,y)*y;
}

signed main(){
  ll N,M,K;
  ull ans=INF;
  cin>>N>>M;
  vector<ull> A(N);
  vector<ull> B(M);
  vector<ll>r(2);
  vector<ll>m={N,M};
  K=lcm(N,M);
  for(ull i=0;i<N;i++)cin>>A.at(i);
  for(ull i=0;i<M;i++)cin>>B.at(i);
  for(ull i=0;i<N;i++)for(ull j=0;j<M;j++){
    if(A.at(i)==B.at(j)){
      if(i==j)ans=min(ans,i+1);
      else{
        r.at(0)=i+1;
        r.at(1)=j+1;
        Pll a=crt(r,m);
        if(a.second==0){
          continue;
        }
        if(a.first==0){
          ans=min(ans,K);
          continue;
        }
        ans=min(ans,(ull)a.first%a.second);
      }
    }
  }
  if(ans==INF)printf("-1\n");
  else printf("%lld\n",ans);
  return 0;
}