#include "bits/stdc++.h"
#define ALL(obj) (obj).begin(),(obj).end()
#define RALL(obj) (obj).rbegin(),(obj).rend()
#define REP(i, n) for(int i = 0; i < (int)(n); i++)
#define REPR(i, n) for(int i = (int)(n); i >= 0; i--)
#define FOR(i,n,m) for(int i = (int)(n); i < int(m); i++)
using namespace std;
typedef long long ll;
const int MOD = 1e9 + 7;
const int INF = MOD - 1;
const ll LLINF = 4e18;

int myhash(int n) {
    if (n <= 9) return n;
    int k = 0;
    while (n > 0) {
        k += n % 10;
        n /= 10;
    }
    return myhash(k);
}

int main() {
    int k,N; cin >> k >> N;
    // エラトステネスの篩
    // N以下の素数   
    vector<bool> isprime(N + 1, true);
    vector<int> prime;
    isprime[0] = isprime[1] = false;
    for (int i = 2; i*i <= N; i++)
    {
        if (isprime[i]) {
            for (int j = i + i; j <= N; j += i)
            {
                isprime[j] = false;
            }
        }
    }
    for (int i = k; i <= N; i++)
    {
        if (isprime[i]) {
            prime.push_back(i);
        }
    }
    vector<int> value(prime.size());
    REP(i, prime.size()) {
        value[i] = myhash(prime[i]);
    }
    int l = 0, r = 0;
    bool f[10];
    int m = 0;
    int ans;
    REP(i, 10) f[i] = false;
    while(r < value.size()) {
        while (r < value.size() && !f[value[r]]) {
            f[value[r++]] = true;
        }
        if (m <= r - l) {
            m = r - l;
            ans = prime[l];
        }
        while (r < value.size() && l < r) {
            f[value[l++]] = false;
            if (value[r] == value[l - 1]) break;
        }
    }
    cout << ans << endl;
    getchar(); getchar();
}