import java.math.*;
import java.util.*;

class Main {
	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] num = new int[n];
        for(int i=0;i<n;i++){
        	num[i]=sc.nextInt();
        }
        ArrayList<Integer> sosuu = new ArrayList<>();
        sosuu.add(0);
        boolean[] sosu=new boolean[5000001];
        for(int i=2;i<=5000000;i++){
        	if(!sosu[i]){
        		sosuu.add(i);
        		for(int j=i*2;j<=5000000;j+=i){
        			sosu[j]=true;
        		}
        	}
        }
        sosuu.add(5000001);
        int target=0;
        for(int i=0;i<n;i++){
        	target |= (1<<num[i]);
        }
        
        int rou=1;
        int hi = 1;
        int cur =0;
        int ans=-1;
        for(int i=1;i<sosuu.size()-1;i++){
        	int temp = sosuu.get(i);
        	int temp1=0;
        	while(temp>0){
        		temp1 |=(1<<(temp%10));
        		temp/=10;
        	}
        	cur |= temp1;
        	hi=i;
        	if(target==cur){
        		ans=Math.max(ans, sosuu.get(hi+1)-sosuu.get(rou-1)-2);
        	}else if((target|cur)-target>0){
        		rou=hi=i+1;
        		cur=0;
        	}
        }
        System.out.println(ans);
        
    }
}