import java.io.*;
import java.util.*;

public class Main {

    static boolean[] a = new boolean[10];

    public static void main(String[] args) throws Exception {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        for (int i = 0; i < n; i++) {
            a[sc.nextInt()] = true;
        }

        ArrayList<Integer> prime = getPrime();

        int miniMax = Integer.MIN_VALUE;

        for (int i = 0; i < prime.size(); i++) {
            TreeMap<Integer, Integer> nums = getNum(prime.get(i));

            if (!isTrue(nums)) {
                continue;
            }

            int miniIndex = i;
            int maxIndex = 0;

            i++;

            boolean[] tmpA = a.clone();
            cieve(tmpA, nums);

            for (; i < prime.size(); i++) {
                nums = getNum(prime.get(i));

                if (!isTrue(nums)) {
                    break;
                }
                maxIndex = i;
                cieve(tmpA, nums);
            }

            boolean include = true;

            for (boolean a : tmpA) {
                if (a) {
                    include = false;
                    break;
                }
            }
            if (!include) {
                continue;
            }

            int min;
            int max;

            if (miniIndex == 0) {
                min = 1;
            } else {
                min = prime.get(miniIndex - 1) + 1;
            }

            if (maxIndex == prime.size() - 1) {
                max = 5000000;
            } else {
                max = prime.get(maxIndex + 1) - 1;
            }

            if (miniMax < max - min) {
                miniMax = max - min;
            }
        }

        if (miniMax == Integer.MIN_VALUE) {
            System.out.println(-1);
        } else {
            System.out.println(miniMax);
        }
    }

    private static ArrayList<Integer> getPrime() {
        boolean[] cieve = new boolean[5000001];

        cieve[0] = true;
        cieve[1] = true;

        int max = (int) Math.sqrt(5000000);

        for (int i = 2; i <= max; i++) {

            if (cieve[i]) {
                continue;
            }
            for (int j = i; j * i < 5000000; j++) {
                cieve[j * i] = true;
            }
        }

        ArrayList<Integer> ret = new ArrayList();

        for (int i = 0; i < 5000000; i++) {
            if (!cieve[i]) {
                ret.add(i);
            }
        }

        return ret;
    }

    private static TreeMap<Integer, Integer> getNum(int num) {
        TreeMap<Integer, Integer> ret = new TreeMap();

        while (num != 0) {
            ret.put(num % 10, 0);
            num = num / 10;
        }

        return ret;
    }

    private static boolean isTrue(TreeMap<Integer, Integer> nums) {
        for (int num : nums.keySet()) {
            if (!a[num]) {
                return false;
            }
        }
        return true;
    }

    private static void cieve(boolean[] tmpA, TreeMap<Integer, Integer> nums) {
        for (int num : nums.keySet()) {
            tmpA[num] = false;
        }
    }
}