import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Deque;
import java.util.HashMap;
import java.util.InputMismatchException;
import java.util.Map;
import java.util.PriorityQueue;
import java.math.BigInteger;
    
public class Main{

static final InputStream in=System.in;
static final PrintWriter out=new PrintWriter(System.out);
static final int INF=Integer.MAX_VALUE/2;
static final long LINF=Long.MAX_VALUE/2;
static int K,N;
static boolean[] used=new boolean[10];

public static void main(String[] args) throws IOException{
InputReader ir=new InputReader(in);
K=ir.nextInt();
N=ir.nextInt();
boolean[] p=sieveOfEratosthenes();
int[] plist=new int[N];
int t=0;
for(int i=K;i<=N;i++) if(p[i]) plist[t++]=i;
int[] hashlist=new int[t];
for(int i=0;i<t;i++) hashlist[i]=calc(plist[i]);
int cnt,res,l,r,ans;
cnt=res=1;
l=r=0;
ans=-1;
used[hashlist[0]]=true;
while(true){
r++;
if(r>=t){
ans=l;
break;
}
if(!used[hashlist[r]]){
cnt++;
used[hashlist[r]]=true;
}
else{
if(res<cnt){
res=cnt;
ans=l;
}
for(int i=r-1;;i--){
if(hashlist[i]==hashlist[r]){
l=i+1;
cnt=r-i;
break;
}
}
}
}
out.println(plist[ans]);
out.flush();
}

public static int calc(int a){
int cnt=0;
while(a/10>0){
cnt+=a%10;
a/=10;
}
return cnt;
}

public static boolean[] sieveOfEratosthenes(){
boolean[] res=new boolean[N+1];
Arrays.fill(res,true);
res[0]=res[1]=false;
for(int i=2;i<=Math.sqrt(N);i++){
if(res[i]) for(int j=i+i;j<=N;j+=i) res[j]=false;
}
return res;
}

static class InputReader {
private InputStream in;
private byte[] buffer=new byte[1024];
private int curbuf;
private int lenbuf;

public InputReader(InputStream in) {this.in=in;}
  
public int readByte() {
if(lenbuf==-1) throw new InputMismatchException();
if(curbuf>=lenbuf){
curbuf= 0;
try{
lenbuf=in.read(buffer);
}
catch (IOException e) {
throw new InputMismatchException();
}
if(lenbuf<=0)
return -1;
}
return buffer[curbuf++];
}

public boolean isSpaceChar(int c){return !(c>=33&&c<=126);}

private int skip() {int b; while((b = readByte())!=-1&&isSpaceChar(b)); return b;}

public String next() {
int b=skip();
StringBuilder sb=new StringBuilder();
while(!isSpaceChar(b)){
sb.appendCodePoint(b);
b=readByte();
}
return sb.toString();
}
 
public int nextInt() {
int c=readByte();
while (isSpaceChar(c)) c=readByte();
boolean minus=false;
if (c=='-') {
minus=true;
c=readByte();
}
int res=0;
do{
if(c<'0'||c>'9') throw new InputMismatchException();
res=res*10+c-'0';
c=readByte();
}while(!isSpaceChar(c));
return (minus)?-res:res;
}

public long nextLong() {
int c=readByte();
while (isSpaceChar(c)) c=readByte();
boolean minus=false;
if (c=='-') {
minus=true;
c=readByte();
}
long res = 0;
do{
if(c<'0'||c>'9') throw new InputMismatchException();
res=res*10+c-'0';
c=readByte();
}while(!isSpaceChar(c));
return (minus)?-res:res;
}

public int[] toIntArray(int n){
int[] a=new int[n];
for(int i=0;i<n;i++) a[i]=nextInt();
return a;
}
}
}