#include<iostream>
#include<vector>
#include<string>
#include<algorithm>	
#include<map>
#include<set>
#include<utility>
#include<cmath>
#include<cstring>
#include<queue>
#include<stack>
#include<cstdio>
#include<sstream>
#include<iomanip>
#include<assert.h>
#define loop(i,a,b) for(int i=a;i<b;i++) 
#define rep(i,a) loop(i,0,a)
#define pb push_back
#define mt make_tuple
#define all(in) in.begin(),in.end()
#define shosu(x) fixed<<setprecision(x)
using namespace std;
//kaewasuretyuui
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vp;
typedef vector<vp> vvp;
typedef vector<string> vs;
typedef vector<double> vd;
typedef tuple<int,int,int> tp;
typedef vector<tp> vt;
typedef vector<vd> vvd;
typedef pair<int,pii> pip;
typedef vector<pip>vip;
const double PI=acos(-1);
const double EPS=1e-7;
const int inf=1e9;
const ll INF=1e16;
int dx[4]={0,1,0,-1};
int dy[4]={1,0,-1,0};
#define MAX 200010
int sos[MAX]={1,1,0};
vp sosu;
int S,T;
void init(){
	for(int i=2;i*i<=MAX;i++)if(!sos[i])
	for(int j=i*2;j<MAX;j+=i)sos[j]=true;
	loop(i,S,T+1)if(sos[i]==0)sosu.pb({i,0});
}
int main(){
	cin>>S>>T;
	init();
	rep(i,sosu.size()){
		int t=sosu[i].first;
		while(t>=10){
			int a=0;
			while(t){
				a+=t%10;
				t/=10;
			}
			t=a;
		}
		sosu[i].second=t;
	}
	int out=0,ma=0;
	int co[10]={0};
	int s=0,t=0;
	while(t<sosu.size()){
		while(t<sosu.size()&&co[sosu[t].second]==0)co[sosu[t++].second]++;
		if(ma<=t-s){
			ma=t-s;
			out=sosu[s].first;
		}
		co[sosu[s].second]--;
		s++;
	}
	cout<<out<<endl;
}