import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Scanner;
import java.util.Set;
import java.util.TreeSet;

public class Main {
	
	public static void update(int[] count, String str, boolean add){
		for(final char ch : str.toCharArray()){
			count[Character.getNumericValue(ch)] += (add ? 1 : -1);
		}
	}
	
	public static boolean valid_range(int[] count, Set<Integer> valid){
		for(int i = 0; i < count.length; i++){
			if(valid.contains(i)  && count[i] <= 0){ return false; }
			if(!valid.contains(i) && count[i]  > 0){ return false; }
		}
		
		return true;
	}
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		final int N = sc.nextInt();
		Set<Integer> valid_set = new HashSet<Integer>();
		for(int i = 0; i < N; i++){
			valid_set.add(sc.nextInt());
		}
		
		final int MAX = 5000000;
		TreeSet<Integer> prime_tree = new TreeSet<Integer>();
		boolean[] is_prime = new boolean[MAX + 1];
		Arrays.fill(is_prime, true);
		is_prime[0] = is_prime[1] = false;
		
		for(int i = 2; i <= MAX; i++){
			if(!is_prime[i]){ continue; }
			
			prime_tree.add(i);
			for(int j = i * 2; j <= MAX; j += i){
				is_prime[j] = false;
			}
		}
		//System.out.println(valid_set);
		
		int lower = 1, upper = 1; // [lower, upper]
		int[] count = new int[10];
		int max = Integer.MIN_VALUE;
		while(lower <= upper){
			//System.out.println("[" + lower + ", " + upper + "] + " + Arrays.toString(count));
			
			if(valid_range(count, valid_set) && upper <= MAX){
				max = Math.max(max, (prime_tree.ceiling(upper) - 1) - (prime_tree.floor(lower - 1) + 1));
				//System.out.println(max);
				upper++;
				if(is_prime[upper]){ update(count, Integer.toString(upper), true); }
			}else if(lower < MAX){
				if(is_prime[lower]){ update(count, Integer.toString(lower), false); }
				lower++;
				
				if(lower > upper){
					if(is_prime[lower]){ update(count, Integer.toString(lower), true); }
					upper = lower;
				}
			}else{
				break;
			}
		}
		
		System.out.println(max == Integer.MIN_VALUE ? -1 : max);
	}

}