#include <bits/stdc++.h> 

#define int long long

#define REP(i, b) for(int i = 0; i < (b); i++)
#define REPS(i, b) for(int i = 1; i <= (b); i++)
#define ALL(v) (v).begin(), (v).end()

using namespace std;

using pi = pair<int, int>;
using vi = vector<int>;
using vs = vector<string>;
using vb = vector<bool>;
using vpi = vector<pi>;
using vvi = vector<vi>;
using vvb = vector<vb>;

const int INF = 1e10;
const int MOD = 1e9+7;

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

int h(int n)
{
    int res = 0;
    while(n > 0)
    {
        res += n % 10;
        n /= 10;
    }
    if(res >= 10) return h(res);
    return res;
}

signed main()
{
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(10);

    int K, N; cin >> K >> N;
    vb isPrime(200001, true); isPrime[0] = isPrime[1] = false;
    for(int i = 2; i <= 200000; i++)
    {
        if(isPrime[i])
        {
            for(int j = 2*i; j <= 200000; j += i) isPrime[j] = false;
        }
    }

    vpi table;
    for(int i = K; i <= N; i++)
    {
        if(isPrime[i]) table.push_back(make_pair(i, h(i)));
    }

    vb v(10, false);
    int r = 0, x = table[0].first;
    int len = 0;
    for(int l = 0; l < table.size(); l++)
    {
        while(r < table.size() && !v[table[r].second])
        {
            v[table[r].second] = true;
            r++;
        }
        if(len <= r-l)
        {
            len = r-l;
            x = table[l].first;
        }
        v[table[l].second] = false;
    }
    cout << x << endl;
}