#include<iostream>
#include<sstream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<string>
#include<vector>
#include<cmath>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<numeric>
#include<functional>
#include<complex>

using namespace std;
#define BET(a,b,c) ((a)<=(b)&&(b)<(c))
#define FOR(i,n) for(int i=0,i##_end=(int(n));i<i##_end;i++)
#define SZ(x) (int)(x.size())
#define ALL(x) (x).begin(),(x).end()
#define MP make_pair
#define FOR_EACH(it,v) for(__typeof(v.begin()) it=v.begin(),it_end=v.end() ; it != it_end ; it++)
typedef vector<int> VI;
typedef vector<VI> VVI;

int main()
{
    VI isprime(5000000+1, 1), use(5000000+1);
    VI primes;
    isprime[0] = isprime[1] = 0;
    use[1] = 1<<1;
    for(int i=2;i<SZ(isprime);i++){
        use[i] |= 1<<(i%10);
        if(i/10>0) use[i] |= use[i/10];
        if(!isprime[i]) continue;
        primes.push_back(i);
        for(int j=i+i;j<SZ(isprime);j+=i){
            isprime[j] = 0;
        }
    }

    int n;
    cin>>n;
    int mask = 0;
    FOR(i,n) {
        int a;
        cin>>a;
        mask |= (1<<a);
    }
    int ans = -1 ;
    int left = 1;
    int flag = 0;
    FOR(i,SZ(primes)){
        if((~mask) & use[primes[i]]) {
            left = primes[i] + 1;
            flag = 0 ;
        }else {
            flag |= use[primes[i]];
            if(flag == mask){
                //cout<<primes[i]<<" "<<use[primes[i]]<<endl;
                if(i + 1 < SZ(primes)){
                    ans = max(ans, primes[i+1] - 1 - left);
                }else{
                    ans = max(ans, 5000000 - left);
                }
            }
        }
    }
    cout<<ans<<endl;

    return 0;
}