#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <set>
#include <map>
#include <queue>
#include <climits>
#include <cstdlib>
#include <cassert>
using namespace std;

#define REP(i,n) for(int i=0;i<n;i++)
#define INF INT_MAX/3
#define LINF LLONG_MAX/3
#define MP make_pair
#define PB push_back
#define ALL(v) (v).begin(),(v).end()

typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;

int N,K;
bool sosu[200001];

int f(int n){
    if(n<10) return n;
    int s = 0;
    while(n>0){
        s += n%10;
        n /= 10;
    }
    return f(s);
}

int main(){
    cin >> K >> N;
    for(int i=2;i<=N;i++) sosu[i]=true;

    for(int i=2;i*i<=N;i++){
        if(!sosu[i]) continue;
        for(int j=i*2;j<=N;j+=i){
            sosu[j] = false;
        }
    }

    vector<int> s;
    for(int i=K;i<=N;i++) if(sosu[i]) s.push_back(i);
    vector<int> cnt(s.size());
    for(int i=0;i<s.size();i++) cnt[i] = f(s[i]);

    //for(int i=0;i<s.size();i++) printf("(%02d,,%03d,%d) ",i,s[i],cnt[i]);

    vector<bool> use(10,false);
    int ans = 0;
    int len = 0;
    int l=0,r=0;
    for(r=0;r<s.size();r++){
        if(use[cnt[r]]){
            for(;;){
                if(cnt[l]==cnt[r]) break;
                use[cnt[l]]=false;
                l++;
            }
            if(l<r){
                while(cnt[l]==cnt[r]) l++;
            }
        }
        if(l>r) l=r;
        if(len<=r-l+1){
            ans = l;
            len = r-l+1;
        }
        use[cnt[r]]=true;
    }
    cout << s[ans] << endl;
}