#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long int ll;
typedef long double ld;
#define max 1e18
#define FOR(i,l,r) for(ll i=l;i<r;i++)
#define REP(i,n) FOR(i,0,n)
#define RFOR(i,l,r) for(ll i=r-1;i>=l;i--)
#define RREP(i,n) RFOR(i,0,n)
#define ALL(x) x.begin(),x.end()
#define P pair<ll,ll>
#define F first
#define S second
#define BS(A,x) binary_search(ALL(A),x)
#define LB(A,x) (ll)(lower_bound(ALL(A),x)-A.begin())
#define UB(A,x) (ll)(upper_bound(ALL(A),x)-A.begin())
template<typename T>using min_priority_queue=priority_queue<T,vector<T>,greater<T>>;
using mint=modint1000000007;
bool prime(ll N){if(N<2)return 0;ll d=2;while(d*d<=N){if(N%d==0)return 0;d++;}return 1;}
ll hush(ll N){if(N<10)return N;ll res=0;while(N){res+=N%10;N/=10;}return hush(res);}
signed main(){
  ll K,N,ans,m=0,r=0;cin>>K>>N;vector<P>A;vector<bool>X(10,1);
  FOR(i,K,N+1)if(prime(i))A.push_back(P(hush(i),i));
  REP(i,A.size()){
    while(r<A.size()&&X[A[r].F])X[A[r++].F]=0;
    if(m<=r-i){ans=A[i].S;m=r-i;}X[A[i].F]=1;
  }
  cout<<ans<<endl;
  return 0;
}