#include<algorithm>
#include<complex>
#include<ctype.h>
#include<iomanip>
#include<iostream>
#include<fstream>
#include<map>
#include<math.h>
#include<numeric>
#include<queue>
#include<set>
#include<stack>
#include<stdio.h>
#include<string>
#include<string>
#include<vector>

using namespace std;
typedef long long ll;

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("Yes")
#define p_no() p("No")

const ll mod = 1e9 + 7;
const ll inf = 1e18;

template < typename T >
void vprint(T &V){
	for(auto v : V){
    	cout << v << " ";
	}
	cout << endl;
}

const int N_MAX = 200010;
bool is_prime[N_MAX];

// エラトステネスのふるい
void Eratosthenes(){
    FOR(i, 0, N_MAX){
        is_prime[i] = true;
    }
    is_prime[0] = false;
    is_prime[1] = false;
    FOR(i, 2, N_MAX){
        if(is_prime[i]==1){
            int p = i;
            int step_p = p;
            // それの倍数を消していく
            while(p < N_MAX){
                p += step_p;
                if(p<N_MAX){
                    is_prime[p] = 0;
                }
            }
        }
    }
}

ll h(ll n){
    if(n<10){
        return n;
    }else{
        ll sum = 0;
        while(n!=0){
            sum += n%10;
            n /= 10;
        }
        return h(sum);
    }
    return -1;
}

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

    // input
    ll K, N;
    cin >> K >> N;

    Eratosthenes();

    vector<ll> primes;
    FOR(i, K, N+1){
        if(is_prime[i]){
            primes.push_back(i);
        }
    }
    
    vector<ll> H;
    for(ll p : primes){
        H.push_back(h(p));
    }
    
    ll max_len = 0;
    ll max_len_index = -1;
    
    ll L = H.size();
    FOR(i, 0, L){
        vector<bool> have(10, false);
        FOR(j, 0, 15){
            ll index = i + j;
            if(index > L-1){
                ll len = j;
                if(len >= max_len){
                    max_len = len;
                    max_len_index = i;
                }
                break;
            }
            
            ll val = H[index];
            if(have[val]){
                // これ以上見ても意味がない
                ll len = j;
                if(len >= max_len){
                    max_len = len;
                    max_len_index = i;
                }
                break;
            }else{
                have[val] = true;
            }
        }
    }

    ll ans = primes[max_len_index];
    p(ans);
    
    return 0;
}