#include<iostream>
#include<sstream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<string>
#include<vector>
#include<cmath>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<numeric>
#include<functional>
#include<complex>

using namespace std;
#define BET(a,b,c) ((a)<=(b)&&(b)<(c))
#define FOR(i,n) for(int i=0,i##_end=(int(n));i<i##_end;i++)
#define SZ(x) (int)(x.size())
#define ALL(x) (x).begin(),(x).end()
#define MP make_pair
#define FOR_EACH(it,v) for(__typeof(v.begin()) it=v.begin(),it_end=v.end() ; it != it_end ; it++)
typedef vector<int> VI;
typedef vector<VI> VVI;

int main()
{
    int K,N;
    cin>>K>>N;
    VI isPrime(N+1, true);
    isPrime[0] = isPrime[1] = false;
    for(int i=2;i<=N;i++){
        if(!isPrime[i]) continue;
        for(int j=i+i;j<=N;j+=i) isPrime[j] = false;
    }
    VI hash(N+1);
    FOR(i,N+1){
        if(i < 10) hash[i] = i;
        else {
            hash[i] = (hash[i/10] + i % 10);
            if(hash[i] >= 10) {
                hash[i] -= 10;
                hash[i] += 1;
            }
        }
    }
    int maxlen = 0, ans = -1;
    for(int i=K;i<=N;i++){
        if(!isPrime[i]) continue;
        VI f(10);
        int len = 0 ;
        for(int j=i;j<=N;j++){
            if(!isPrime[j]) continue;
            if(f[hash[j]]) break;
            f[hash[j]]++;
            len++;
        }
        if(maxlen <= len){
            maxlen = len;
            ans = i;
        }
    }
    cout<<ans<<endl;
    return 0;
}