#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i < n; ++i)
using ll = long long;
using P = pair<int,int>;
bool subset(set<int> main, set<int> sub){
  for (auto &&i : sub)
    if(main.find(i)==main.end()) return false;
  return true;
}
bool equalset(set<int>s1,set<int>s2){
  if(s1.size()!=s2.size())return false;
  return (subset(s1,s2));
}
// Sieve of Eratosthenes
struct Sieve {
  int n;
  vector<int> f, primes;
  Sieve(int n=1):n(n), f(n+1) {
    f[0] = f[1] = -1;
    for (ll i = 2; i <= n; ++i) {
      if (f[i]) continue;
      primes.push_back(i);
      f[i] = i;
      for (ll j = i*i; j <= n; j += i) {
        if (!f[j]) f[j] = i;
      }
    }
  }
  bool isPrime(int x) { return f[x] == x;}
  vector<int> factorList(int x) {
    vector<int> res;
    while (x != 1) {
      res.push_back(f[x]);
      x /= f[x];
    }
    return res;
  }
  vector<P> factor(int x) {
    vector<int> fl = factorList(x);
    if (fl.size() == 0) return {};
    vector<P> res(1, P(fl[0], 0));
    for (int p : fl) {
      if (res.back().first == p) {
        res.back().second++;
      } else {
        res.emplace_back(p, 1);
      }
    }
    return res;
  }
};
set<int> num_to_nums(int num){
   set<int> nums;
   while(num>0){
      nums.insert(num%10);
      num/=10;
   }
   return nums;
}
int main() {
  Sieve primes(5000000);
  int N;cin>>N;
  set<int> now,target;
  int l=1,r=1,ans=0;
  rep(i,N){
    int Ai;cin>>Ai;
    target.insert(Ai);
  }
  primes.primes.push_back(5000001);
  for (int i = 0; i < primes.primes.size()-1; i++)
  {
    now.merge(num_to_nums(primes.primes[i]));
    if(subset(target,now)){
      if(equalset(target,now))
        r=primes.primes[i+1]-1;
    }
    else{
      l=primes.primes[i]+1;
      now.clear();
    }
    ans=max(ans,r-l);
  }
  cout<<(ans==0?-1:ans)<<endl;
}