#include<bits/stdc++.h>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)

int K, N;
int H[200001];
bool sieve[200001] = {};
vector<int> A;

int main() {
    int K, N; cin >> K >> N;

    rep(i, 10) H[i] = i;
    for (int i = 10; i <= 200000; i++) {
        int p = i, buf = 0;
        while (p) { buf += p % 10; p /= 10; }
        H[i] = H[buf];
    }

    sieve[0] = sieve[1] = true;
    for (int i = 2; i < 1000; i++) {
        if (sieve[i]) continue;
        for (int j = i * i; j <= 200000; j += i) sieve[j] = true;
    }

    for (int i = K; i <= N; i++) if (!sieve[i]) A.push_back(i);

    int ans = 0, len = 0;
    rep(i, A.size()) {
        bitset<10> f;
        int lentmp = 0;
        for (int j = i; j < A.size(); j++) {
            if (f.test(H[A[j]])) break;
            lentmp++;
            f.set(H[A[j]]);
        }
        if (len <= lentmp) { len = lentmp; ans = A[i]; }
    }

    cout << ans << endl;

    return 0;
}