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

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int target = 0;
        for (int i = 0; i < n; i++) {
            target += (1 << sc.nextInt());
        }
        ArrayList<Integer> primes = new ArrayList<>();
        primes.add(0);
        boolean[] isNotPrimes = new boolean[5000001];
        for (int i = 2; i < isNotPrimes.length; i++) {
            if (!isNotPrimes[i]) {
                primes.add(i);
                for (int j = 2; j * i < isNotPrimes.length; j++) {
                    isNotPrimes[j * i] = true;
                }
            }
        }
        primes.add(5000001);
        int left = 1;
        int[] counts = new int[10];
        int ans = -1;
        for (int i = 1; i < primes.size() - 1; i++) {
            addCount(counts, primes.get(i));
            int current = getMask(counts);
            if (current == target) {
                ans = Math.max(ans, primes.get(i + 1) - primes.get(left - 1) - 2);
            } else if ((current ^ (current & target)) > 0) {
                left = i + 1;
                Arrays.fill(counts, 0);
            }
        }
        System.out.println(ans);
    }
    
    static int getMask(int[] counts) {
        int mask = 0;
        for (int i = 0; i < counts.length; i++) {
            if (counts[i] > 0) {
                mask += (1 << i);
            }
        }
        return mask;
    }
    
    static void addCount(int[] counts, int value) {
        while (value > 0) {
            counts[value % 10]++;
            value /= 10;
        }
    }    
}

class Utilities {
    static String arrayToLineString(Object[] arr) {
        return Arrays.stream(arr).map(x -> x.toString()).collect(Collectors.joining("\n"));
    }
    
    static String arrayToLineString(int[] arr) {
        return String.join("\n", Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new));
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public int[] nextIntArray() throws Exception {
        return Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
    
}