#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

using ll = long long;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

struct ExtendedSieve{
    vector<int> table;
    const int n;

    ExtendedSieve(int n) : n(n) {
        table.assign(n + 1, 0);
        table[0] = table[1] = 1;
        for(int i = 2; i <= n; ++i){
            if(table[i] > 0)    continue;
            table[i] = i;
            for(int j = i + i; j <= n; j += i){
                if(table[j] == 0)   table[j] = i;
            }
        }
    }

    int operator[](const int& k){
        return table[k];
    }

    bool is_prime(int x){
        if(x < 2)   return false;
        return x == table[x];
    }

    map<int, int> prime_factorization(int x){
        map<int, int> res;
        while(x > 1){
            ++res[table[x]];
            x /= table[x];
        }
        return res;
    }
};

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int K, N;
    cin >> K >> N;
    ExtendedSieve sieve(N);
    vector<int> hashval(N + 1, -1);
    vector<int> compress, prime;
    set<int> st;
    for(int i = K; i <= N; ++i){
        if(!sieve.is_prime(i))  continue;
        hashval[i] = i;
        while(hashval[i] >= 10){
            int sum = 0;
            while(hashval[i] > 0){
                sum += hashval[i] % 10;
                hashval[i] /= 10;
            }
            hashval[i] = sum;
        }
        st.emplace(hashval[i]);
        prime.emplace_back(i);
    }
    int P = prime.size(), S = st.size();
    for(int i = P - 1; i >= 0; --i){
        set<int> st2;
        for(int j = 0; j < S; ++j){
            if(i + j >= P)  break;
            st2.emplace(hashval[prime[i + j]]);
        }
        if((int)st2.size() == S){
            cout << prime[i] << endl;
            return 0;
        }
    }

    return 0;
}