#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }


constexpr int LIM = 30010;
int lpf[LIM];

int M, N;
vector<int> A, B;

bitset<LIM> hasA, hasB;

int len;
vector<int> ps, es;

bool dfs(int i, int x, int y) {
  if (i == len) {
    if (hasA[(int)sqrt(y)] && hasB[(int)sqrt(x / y)]) {
      return true;
    }
    return false;
  } else {
    for (int e = 0; ; ++e) {
      if (dfs(i + 1, x, y)) return true;
      if (e == es[i]) break;
      y *= ps[i];
    }
    return false;
  }
}

int main() {
  iota(lpf, lpf + LIM, 0);
  for (int p = 2; p < LIM; ++p) if (lpf[p] == p) {
    for (int n = 2 * p; n < LIM; n += p) chmin(lpf[n], p);
  }
  
  for (; ~scanf("%d%d", &M, &N); ) {
    A.resize(M); for (int i = 0; i < M; ++i) scanf("%d", &A[i]);
    B.resize(N); for (int i = 0; i < N; ++i) scanf("%d", &B[i]);
    
    hasA.reset(); for (int i = 0; i < M; ++i) hasA[A[i]] = true;
    hasB.reset(); for (int i = 0; i < N; ++i) hasB[B[i]] = true;
    
    int ans = 0;
    if (!(A[0] == 1 && B[0] == 1)) {
      ans = 1;
    } else {
      for (int c = 1; ; ++c) if (!hasA[c] && !hasB[c]) {
        // [c^2, (c+1)^2)
        const int lb = c * c;
        const int ub = (c + 1) * (c + 1);
        vector<vector<int>> sieve(ub - lb);
        for (int p = 2; p < LIM; ++p) if (lpf[p] == p) {
          for (int x = (lb + p - 1) / p * p; x < ub; x += p) {
            const int pos = x - lb;
            sieve[pos].push_back(p);
          }
        }
        for (int x = lb; x < ub; ++x) {
          const int pos = x - lb;
          int xx = x;
          ps.clear();
          es.clear();
          for (const int p : sieve[pos]) {
            int e = 0;
            do {
              ++e;
              xx /= p;
            } while (xx % p == 0);
            ps.push_back(p);
            es.push_back(e);
          }
          if (xx > 1) {
            ps.push_back(xx);
            es.push_back(1);
          }
          len = ps.size();
// cerr<<x<<": "<<ps<<" "<<es<<endl;
          if (!dfs(0, x, 1)) {
            ans = x;
            goto found;
          }
        }
        assert(false);
      }
     found:{}
    }
    printf("%d\n", ans);
  }
  return 0;
}