#include <bits/stdc++.h>
using namespace std;

int f(int a){
  if(a<10)return a;
  int res=0;
  while(a){
    res+=a%10;
    a/=10;
  }
  return f(res);
}
bool prime(int a){
  if(a<2)return 0;
  for(int i=2;i*i<=a;i++)if(a%i==0)return 0;
  return 1;
}

signed main(){
  int k,n;cin>>k>>n;
  int mx=0,ans=0,now=0;
  vector<int> v(10,0);
  vector<int> w;
  for(int i=k;i<=n;i++)if(prime(i))w.push_back(i);
  for(int j=0;j<w.size();j++){
    int a=f(w[j]);
    while(v[a])v[f(w[now++])]--;
    v[a]++;
    if(mx<=j-now)mx=j-now,ans=w[now];
  }
  cout<<ans<<endl;
}