#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>

int isPrime(int x){
    if(x == 1){return false;}

    for(int i=2;i*i<=x;i++){
        if(x % i == 0){return false;}
    }
    return true;
}

int hash(int x){
    std::string s = std::to_string(x);
    while(s.size() > 1){
        int sum = 0;
        for(auto c : s){sum += c - '0';}
        s = std::to_string(sum);
    }

    return s[0] - '0';
}

int main(){
    int K, N;
    scanf("%d %d", &K, &N);

    std::vector<int> primes;
    for(int i=K;i<=N;i++){
        if(isPrime(i)){primes.push_back(i);}
    }
    
    int p_length = primes.size();

    std::vector<int> hs;
    for(int i=0;i<p_length;i++){
        hs.push_back(hash(primes[i]));
    }

    int maxLength = 0, first;
    int table[10];
    std::fill(table, table+10, 0);

    for(int i=0,j=0;i<p_length;){
        while(j<p_length && table[hs[j]] == 0){
            table[hs[j]] += 1;
            j += 1;
        }

        if(j-i >= maxLength){
            maxLength = j-i;
            first = primes[i];
        }

        table[hs[i]] -= 1;
        i += 1;
    }

    printf("%d\n", first);
}