#include <iostream>
#include <vector>
int hash(int n){
	if(n<10)return n;
	int m=0;
	while(n){m+=n%10;n/=10;}
	return hash(m);
}
int main(){
	std::vector<bool> seq(210000);seq[0]=seq[1]=0;seq[2]=1;
	for(size_t i=3;i<seq.size();i+=2){seq[i]=1;}
	for(size_t i=3;i<seq.size();i+=2){if(seq[i])for(size_t j=i*2;j<seq.size();j+=i)seq[j]=0;}
	int K,N;std::cin>>K>>N;
	std::vector<int> pri;
	for (int i = K; i <= N; i++) if(seq[i])pri.push_back(i);
	int M=0,Mi=0;
	for(int l=0,r=0,set=0;r<pri.size();){
		if(set&(1<<hash(pri[r]))){
			set&=~(1<<hash(pri[l++]));
		}else{
			set|=1<<hash(pri[r++]);
		}
		if(M<=r-l){M=r-l;Mi=pri[l];}
	}
	std::cout<<Mi;
	return 0;
}