import java.util.ArrayList;
import java.util.BitSet;
import java.util.List;
import java.util.Scanner;


public class Main_yukicoder12 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = 5_000_000;

        List<Integer> primes = new ArrayList<Integer>();

        BitSet sieve = new BitSet();

        primes.add(0);
        primes.add(2);

        for (int i = 1; 2 * i + 1 <= n; i++) {
        	if (!sieve.get(i)) {
        		int p = 2 * i + 1;
        		primes.add(p);

        		for (int j = 1; (i + (2 * i + 1) * j) * 2 + 1 <= n; j++) {
        			sieve.set(i + (2 * i + 1) * j);
        		}
        	}
        }
        primes.add(5_000_001);

        n = sc.nextInt();
        int mask = 0;
        for (int i = 0; i < n; i++) {
        	int a = sc.nextInt();
        	mask |= 0x1 << a;
        }

        int prev = -1;
        int omask = 0;
        int max = -1;
        for (int i = 0; i < primes.size(); i++) {
        	int p = primes.get(i);
        	if (p == 0 || p == 5_000_001) {
        		continue;
        	}

        	int tmp = 0;
        	while (p > 0) {
        		tmp |= 0x1 << p % 10;
        		p /= 10;
        	}

        	if ((tmp | mask) == mask) {
        		if (prev == -1) {
        			prev = i;
        			omask = tmp;
        		} else {
        			omask |= tmp;
        		}

        		if ((omask & mask) == mask) {
        			max = Math.max(max, primes.get(i + 1) - 1 - (primes.get(prev - 1) + 1));
        		}
        	} else {
        		prev = -1;
        	}
        }

        System.out.println(max);

        sc.close();
    }
}