import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Main p = new Main();
	}

	public Main() {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n];
		for(int i=0;i<n;i++){
			a[i] =sc.nextInt();
		}
		solve(a);
	}

	public void solve(int[] a) {		
		int target = 0;
		for(int i=0;i<a.length;i++){
			target |= (1<<a[i]);
		}
		
		boolean[] hurui = new boolean[5000001];
		Arrays.fill(hurui, 2, hurui.length, true);
		ArrayList<Integer> primeList = new ArrayList<Integer>(); 
		primeList.add(0);
		for(int i=2;i<hurui.length;i++){
			if(hurui[i]){
				primeList.add(i);
				for(int j=i*2;j<hurui.length;j+=i){
					hurui[j] = false;
				}
			}
		}
		primeList.add(5000001);
		
		int cur = 0;		
		int res = 0;
		int low = 1;
		int high = 1;
		
		for(int i=1;i<primeList.size()-1;i++){
			int curNum = primeList.get(i);
			int curShift = 0;
			while(curNum>0){
				curShift |= (1<<(curNum%10));
				curNum/=10;
			}
			
			cur |= curShift;
			high = i;
			
			if(target == cur){
				res = Math.max(res, primeList.get(high+1)-primeList.get(low-1)-2);
			}else if((target|cur)-target > 0){
				low = high = i+1;
				cur = 0;
			}
		}
		
		if(res==0)
			System.out.println(-1);
		else
			System.out.println(res);
		
	}

}