#include <bits/stdc++.h>
#define For(i, a, b) for(int (i)=(int)(a); (i)<(int)(b); ++(i))
#define rFor(i, a, b) for(int (i)=(int)(a)-1; (i)>=(int)(b); --(i))
#define rep(i, n) For((i), 0, (n))
#define rrep(i, n) rFor((i), (n), 0)
#define fi first
#define se second
using namespace std;
typedef long long lint;
typedef unsigned long long ulint;
typedef pair<int, int> pii;
typedef pair<lint, lint> pll;
template<class T> bool chmax(T &a, const T &b){if(a<b){a=b; return true;} return false;}
template<class T> bool chmin(T &a, const T &b){if(a>b){a=b; return true;} return false;}
template<class T> T div_floor(T a, T b){
    if(b < 0) a *= -1, b *= -1;
    return a>=0 ? a/b : (a+1)/b-1;
}
template<class T> T div_ceil(T a, T b){
    if(b < 0) a *= -1, b *= -1;
    return a>0 ? (a-1)/b+1 : a/b;
}

constexpr lint mod = 1e9+7;
constexpr lint INF = mod * mod;
constexpr int MAX = 200010;

vector<int> min_factor, prime;

void sieve(int n){
    min_factor.resize(n+1, 0);
    For(i, 2, n+1){
        if(min_factor[i] == 0){
            min_factor[i] = i;
            prime.push_back(i);
        }
        for(int x: prime){
            if(x*i > n || x > i) break;
            min_factor[x*i] = x;
        }
    }
}

vector<pii> prime_f(int n){
    vector<pii> ret;
    while(n > 1){
        if(ret.empty() || ret.rbegin()->fi != min_factor[n]){
            ret.emplace_back(min_factor[n], 1);
        }
        else ++ret.rbegin()->se;
        n /= min_factor[n];
    }
    return ret;
}

bool is_prime(int n){
    return min_factor[n] == n;
}

int dp[MAX];

int f(int n){
    if(dp[n]) return dp[n];
    if(0<=n && n<10) return dp[n] = n;
    int ret = 0;
    while(n){
        ret += n % 10;
        n /= 10;
    }
    return f(ret);
}

int main(){
    int K, n;
    scanf("%d%d", &K, &n);
    sieve(n);
    vector<int> p, h;
    For(i, K, n+1)if(is_prime(i)){
        p.push_back(i);
        h.push_back(f(i));
    }
    int ans, len = 0;
    for(int l=0; l<p.size();){
        int r = l;
        set<int> S;
        while(r < p.size() && S.find(h[r]) == S.end()){
            S.insert(h[r]);
            ++r;
        }
        if(len <= r-l){
            len = r-l;
            ans = p[l];
        }
        S.erase(h[l]);
        ++l;
    }
    printf("%d\n", ans);
}