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

#define rep(i,n) repi(i,0,n)
#define repi(i,a,b) for(int i=int(a);i<int(b);++i)
#define long int64_t
#define ulong uint64_t

const int N = 200000;
int not_prime[N + 1] = {1, 1};
int h[N + 1], p[N + 1], tmp[47];

void prepare()
{
    for (int i = 2; i * i <= N; ++i) {
        if (not_prime[i]) continue;
        for (int j = i * i; j <= N; j += i) {
            not_prime[j] = 1;
        }
    }
    rep(i, 10) h[i] = i;
    repi(i, 10, N + 1) {
        h[i] = h[h[i / 10] + i % 10];
    }
    repi(i, 1, N + 1) {
        if (not_prime[i]) continue;
        p[i] = tmp[h[i]];
        tmp[h[i]] = i;
    }
}

int k, n;

void input()
{
    cin >> k >> n;
}

void solve()
{
    int mx = 0, ans = -1;
    queue<int> q;
    repi(i, k, n + 1) {
        if (not_prime[i]) continue;
        while (not q.empty() and q.front() <= p[i]) q.pop();
        q.push(i);
        if ((int) q.size() >= mx) {
            mx = (int) q.size(), ans = q.front();
        }
    }
    cout << ans << endl;
}

int main()
{
    cin.tie(0);
    ios_base::sync_with_stdio(false);

    prepare();
    input();
    solve();
}