#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

template<class T>
vector<T> divisors(T x) {
  vector<T> res1, res2;
  T d = 1;
  for(; d * d < x; d++) {
    if (x % d == 0) {
      res1.emplace_back(d);
      res2.emplace_back(x / d);
    }
  }
  if (d * d == x) res1.emplace_back(d);
  res1.insert(res1.end(), res2.rbegin(), res2.rend());
  return res1;
}

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  VI a(n), b(m);
  rep(i, n) cin >> a[i];
  rep(i, m) cin >> b[i];
  if (a[0] != 1 || b[0] != 1) {
    cout << 1 << '\n';
    return 0;
  }
  int mx = n + m + 1;
  vector<char> da(mx + 1), db(mx + 1);
  for(int x: a) if (x <= mx) da[x] = 1;
  for(int y: b) if (y <= mx) db[y] = 1;
  int z = 1;
  while(da[z] || db[z]) z++;
  for(int xy = z * z;; xy++) {
    bool ok = false;
    for(int x: divisors(xy)) {
      if (da[int(sqrt(x))] && db[int(sqrt(xy / x))]) {
        ok = true;
        break;
      }
    }
    if (!ok) {
      cout << xy << '\n';
      return 0;
    }
  }
}