#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <algorithm>
#include <sstream>
#include <cmath>
#include <set>
#include <iomanip>
#include <deque>
#include <stdio.h>
using namespace std;

#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 REMOVE(Itr,n) (Itr).erase(remove((Itr).begin(),(Itr).end(),n),(Itr).end())
#define PB_VEC(Itr1,Itr2) (Itr1).insert((Itr1).end(),(Itr2).begin(),(Itr2).end())
#define UNIQUE(Itr) sort((Itr).begin(),(Itr).end()); (Itr).erase(unique((Itr).begin(),(Itr).end()),(Itr).end())
#define LBOUND(Itr,val) lower_bound((Itr).begin(),(Itr).end(),(val))
#define UBOUND(Itr,val) upper_bound((Itr).begin(),(Itr).end(),(val))
typedef long long ll;

/*
ll dp[1<<16];

int main(){
    
    int N; cin>>N;
    dp[(1<<N)-1]=100;
    for (int i=0; i<(1<<N); i++ ){
        
    }
    
    return 0;
}
 */

class Primes {
    vector<bool> sieve; vector<int> prime;
public:
    Primes(int size){
        sieve = *new vector<bool>(size+1,true);
        sieve[0]=sieve[1]=false;
        for(long long i=2;i<size+1;i++){
            if(sieve[i]){
                prime.push_back((int)i);
                for(long long j=i*i;j<size+1;j+=i)sieve[j]=false;
            }
        }
    }
    int size(void) { return (int)prime.size(); }
    int & operator [](int n) { return prime[n]; }
    bool operator ==(int n) { return sieve[n]; }
};

bool judge(set<int> s, int n) {
    while (n!=0) {
        if ( s.find(n%10)==s.end() ) {
            return false;
        }
        n /= 10;
    }
    return true;
}

bool same(set<int> a, set<int> b){
    if(a.size()!=b.size())return false;
    for (auto itr1=a.begin(),itr2=b.begin(); itr1!=a.end(); itr1++,itr2++ ){
        if( *itr1 != *itr2 )  return false;
    }
    return true;
}

void marge(set<int> &a, int n){
    while ( n!=0 ) {
        a.insert(n%10);
        n/=10;
    }
}

int main(){
    
    Primes p(5000000);
    
    int N; cin>>N;
    set<int> unuse;
    REP(i,N){
        int t; cin>>t;
        unuse.insert(t);
    }

    int ans=-1;
    int K=1, L=1;
    set<int> used;
    for (int i=0; i<p.size(); i++ ) {
        if( i!=p.size()-1 ) {
            if ( judge(unuse,p[i]) ){
                L = p[i+1]-1;
                marge(used,p[i]);
                if ( same(unuse,used) ) {
                    ans = max(ans,abs(K-L));
                }
            }else{
                K = p[i]+1;
                used.clear();
            }
        }else {
            if ( judge(unuse,p[i]) ){
                L = 5000000;
                marge(used,p[i]);
                if ( same(used,unuse) ) {
                    ans = max(ans,abs(K-L));
                }
            }
        }
    }
    
    
    if ( ans<=0 ) {
        cout<<-1<<endl;
    }else{
        cout<<ans<<endl;
    }
    
    return 0;
}