#include "bits/stdc++.h"
using namespace std;

/* macro */
#define rep(i,a,b) for(int i=a;i<b;i++)
#define revrep(i,a,b) for(int i = a; i > b; i--)
#define int long long
#define exist(s,e) ((s).find(e)!=(s).end())
#define all(v) (v).begin(), (v).end()
#define each(s,itr) for(auto (itr) = s.begin(); (itr) != s.end(); (itr)++)
#define sum(v) accumulate(all(v), (0LL))
#define isin(a, b, c) (b <= a && a <= c)
#define println cout << "\n";
#define sz(v) (int)v.size()
#define bin(x) static_cast<bitset<16> >(x)



/* alias */
template<class T> using vec = vector<T>;
typedef vector<int> vi;
typedef pair<int, int> pi;
typedef tuple<int, int, int> ti;
typedef map<int, int> mi;
typedef set<int> si;


/* constant */
const int inf = 1LL << 62;
const int mod = 1e9 + 7;
const int dx[8]={1,0,-1,0,-1,1,-1,1};
const int dy[8]={0,1,0,-1,-1,-1,1,1};
const string alphabet = "abcdefghijklmnopqrstuvwxyz";

/* io_method */
int input(){int tmp;cin >> tmp;return tmp;}
string raw_input(){string tmp;cin >> tmp;return tmp;}
template<class T> void printx(T n){cout << n;}
template<class T, class U> void printx(pair<T, U> p){cout << "(" << p.first << "," << p.second << ")";}
template<class T, class U, class V> void printx(tuple<T, U, V> t){cout << "{" << get<0>(t) << "," << get<1>(t) <<"," << get<2>(t) << "}" << endl;}
template<class T> void printx(vector<T> v){cout << "{";rep(i,0,v.size()){printx(v[i]);if(i != v.size()-1)printx(",");}cout << "}";}
template<class T> void print(T n){printx(n);cout << endl;}
template<class T> void print(set<T> s){cout << "{";each(s, e){if(e != s.begin()) printx(",");printx(*e);}cout << "}" << endl;}
template<class T, class U> void print(map<T, U> mp){cout << "{";each(mp, e){cout << "(" << e -> first << "," << e -> second << ")";}cout << "}" << endl;}
template<class T> void printans(vec<T> v){rep(i,0,sz(v)){cout << v[i] << (i == sz(v) - 1 ? "" : " ");}cout << endl;}


/* general_method */
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
template<class T>T cut(T &a, int l, int r){return T(a.begin()+l, a.begin()+r);}

/* main */

vector<int> eratothenes(int n){

    vector<int> ret;

    vector<bool> isprime(n + 1, true);

    for(int i = 2; i < sqrt(n + 1) + 1; i++){
        if(isprime[i]){
            for(int j = 2; i * j < n + 1; j++){
                isprime[i * j] = false;
            }
        }
    }


    for(int i = 2; i < n + 1; i++){
        if(isprime[i]) ret.push_back(i);
    }

    return ret;

}

bool is_prime(const unsigned n){
    switch(n){
        case 0: // fall-through
        case 1: return false;
        case 2: // fall-through
        case 3: return true;
    } 

    if(n%2 == 0) return false;
    if(n%3 == 0) return false;
 

    if(n%6 != 1 && n%6 != 5) return false;



    for(unsigned i=5;i*i<=n;i+=6){
        if(n%i     == 0) return false; // 6n-1
        if(n%(i+2) == 0) return false; // 6n+1
    }

    return true;
}
int n;
int k = 0;
void in(){
    cin >> n;
    rep(i,0,n) k += (1 << (input() - 1));
}

int getbit(int t){
    int ret = 0;
    while(t){
        ret |= (1 << ((t % 10) - 1));
        t /= 10;
    }
    return ret;
}

void solve(){
    
    vi primes = eratothenes(5000000);

    int ans = 0;

    int l = 1;
    int r = 1;
    int bits = 0;
    int cnt = 0;
    while(l < sz(primes)){

        while(r < sz(primes) && ((k | bits) == k)){

            if(k == bits){
                chmax(ans, primes[r] - 1 - (primes[l - 1] + 1));
            }
            int t = getbit(primes[r]);

            bits |= t;
            r++;
            cnt++;
        }

        l = r;
        cnt = 0;
        bits = 0;
    }

    cout << (ans == 0 ? -1 : ans) << endl;

}

signed main(){

    cin.tie(0);
    ios::sync_with_stdio(false);
    in();
    solve();
    
}