#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
using namespace std;

#define RREP(i,s,e) for (i = s; i >= e; i--)
#define rrep(i,n) RREP(i,n,0)
#define REP(i,s,e) for (i = s; i < e; i++)
#define rep(i,n) REP(i,0,n)
#define INF 1e8

typedef long long ll;

int hsh(int x) {
    int tmp = 0;
    if (x < 10)
        return x;
    else {
        while (x >= 10) {
            tmp += x % 10;
            x /= 10;
        }
        return hsh(tmp + x);
    }
}

int main() {
    int i, j, k, n, index, ans, len, mlen;
    bool p[200001];
    set<int> s;
    cin >> k >> n;
    fill(p,p+200000,true);
    p[0] = p[1] = false;
    REP (i,2,1500) {
        if (p[i]) {
            for (j = 2*i; j <= 200000; j+=i)
                p[j] = false;
        }
    }
    index = k;
    while (!p[index]) index++;
    mlen = len = 0;
    REP (i,k,n+1) {
        if (p[i]) {
            int h = hsh(i);
            if (s.count(h)) {
                j = index;
                while (!p[j] || h != hsh(j)) {
                    if (p[j]) {
                        s.erase(hsh(j));
                        len--;
                    }
                    j++;
                }
                index = j+1;
                while (!p[index]) index++;
            }
            else {
                len++;
                s.insert(h);
            }
            if (len >= mlen) {
                mlen = len;
                ans = index;
            }
        }
    }
    cout << ans << endl;
    return 0;
}