#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <cstring>

using namespace std;

bool isPrime[5000001];
int main(){
  vector<int> primes;
  primes.push_back(0);
  memset(isPrime,true,sizeof(isPrime));
  for( int i = 2 ; i < 5000001; i++ ){
    if(isPrime[i]){
      primes.push_back(i);
      for( int j = i+i; j < 5000001;j+=i){
        isPrime[j]=false;
      }
    }
  }
  int N;
  cin >> N;
  bool isOK[10];
  memset(isOK,false,sizeof(isOK));
  for( int i = 0 ; i < N ; i++){
    int a;
    cin >> a;
    isOK[a]=true;
  }
  primes.push_back(5000001);
  int ans = -1;
  for(int i = 1; i+1 < (int)primes.size(); i++ ){
    int p = primes[i];
    set<int> S;
    bool ok = true;
    while(p!=0){
      if( isOK[p%10] == false ){
        ok=false;
        break;
      }
      S.insert(p%10);
      p/=10;
    }
    if( !ok ) continue;
    int j;
    for( j = i+1 ; j+1 < (int) primes.size(); j++ ){
     int p = primes[j];
     bool ok2 = true;
     while(p!=0){
      if( isOK[p%10]==false){
        ok2=false;
        break;
      }
      p/=10;
     }
     if( !ok2 ) break;
    }
    if( S.size() == N ){
      ans = max(ans,primes[j]-1-(primes[i-1]+1));
    }
    i=j;
  }

  cout << ans;
  return 0;
}