import java.util.*;
 

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int K=sc.nextInt();
		int N = sc.nextInt();
		boolean[] nera = new boolean[N+1];
		Arrays.fill(nera, true);
		for(int i=2;i*i<=N;i++){
			if(nera[i]){
				for(int j=i*2;j<=N;j+=i){
					if(nera[j])nera[j]=false;
				}
			}
		}
		ArrayList<Integer> sosuu = new ArrayList<>();
		ArrayList<Integer> ha = new ArrayList<>();
		for(int i=K;i<=N;i++){
			if(i==1) continue;
			if(nera[i]){
				int temp=i;
				sosuu.add(i);
				while(temp>9){
					int temp2=temp;
					temp=0;
					while(temp2!=0){
						temp+=temp2%10;
						temp2=temp2/10;
					}
				}
				ha.add(temp);
			}
		}
		int t=0;
		int s=0;
		Queue<Integer> queue = new LinkedList<>();
		int ans=0;
		int ansmemo=0;
		int temp=0;
		int max=0;
		while(true){			
			while(t<ha.size()){
				 temp = ha.get(t);
				boolean flag = queue.contains(temp);
				queue.offer(temp);
				t++;
				if(t==ha.size()){
					while(true){
						int temp2 = queue.poll();
						s++;
						if(temp2==temp){
							break;
						}
					}
					if(t-s-1>=ans){
						max=sosuu.get(s);
					}
					System.out.println(max);
					return;
				}
				if(flag){
					if(t-s-1>=ans){
						ans=t-s-1;
						max=sosuu.get(s);
					}
					break;
				}
				
			}
			while(true){
				int temp2=queue.poll();
				s++;
				if(temp2==temp){
					temp=0;
					break;
				}
			}			
		}
	}
}