#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <unordered_map>
using namespace std;

int MakePrime(vector<int>& v, int n) {
    bool p[5000001] = {1, 1};
    for(int i = 2; i <= n; i++) {
        if(p[i]) continue;
        v.push_back(i);
        for(int j = i * 2; j <= n; j += i)
            p[j] = true;
    }
    return v.size();
}

int main(void)
{
    const int maxdp = 20001;
    int n;
    vector<int> v;
    int pn = MakePrime(v, 5000000);
    bool a[10] = {0};
    cin >> n;
    for(int i = 0; i < n; i++) {
        int z; cin >> z; a[z] = true;
    }
    int res = -1;
    int k = 0;
    unordered_map<int, bool> um;
    for(int i = 0; i < pn; i++) {
        int t = v[i];
        while(t > 0) {
            int md = t % 10;
            if(!a[md]) {
                if(um.size() == n && (i != k + 1 || k == 0)) {
                    if(k == 0)
                        res = v[i] - 2;
                    else {
                        res = max(res, v[i] - v[k] - 2);
                    }
                }
                k = i;
                um.clear();
                break;
            }
            t /= 10;
            um[md] = true;
        }
    }
    if(um.size() == n && v.size() != k + 1)
        if(k == 0)
            res = v[v.size() - 1];
        else
            res = max(res, v[v.size() - 1] - v[k] - 2);
    cout << res << endl;
    return 0;
}