#include <bits/stdc++.h>
using namespace std;

const int M = 200000;

int myhash(int a) {
    if (a < 10) return a;
    int ret = 0;
    while (a) {
        ret += a % 10;
        a /= 10;
    }
    return myhash(ret);
}

int main() {
    vector<bool> isP(M, true);
    isP[0] = isP[1] = false;
    for (int i = 2; i <= M; i++) {
        if (isP[i]) {
            for (int j = 2*i; j <= M; j += i) {
                isP[j] = false;
            }
        }
    }

    int K, N;
    cin >> K >> N;
    vector<int> ps;
    for (int i = K; i <= N; i++) if (isP[i]) ps.push_back(i);
    set<int> st;
    int ri = 0;
    int id = -1;
    int M_len = -1;
    for (int le = 0; le < ps.size(); le++) {
        while (ri < ps.size() && st.count(myhash(ps[ri])) == 0) {
            st.insert(myhash(ps[ri]));
            ri++;
        }

        if (M_len <= ri - le) {
            M_len = ri - le;
            id = le;
        }

        if (ri == le) ri++;
        else st.erase(myhash(ps[le]));
    }

    cout << ps[id] << endl;
}