#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

vector<int> sieve(int n){
    vector<bool> f(n+1);
    for(int i=3; i<=n; i+=2) f[i] = 1;
    for(int i=3; i<=sqrt(n); i+=2) if(f[i]) for(int j=i*3; j<=n; j+=i) f[j] = 0;
    vector<int> res{2};
    for(int i=3; i<=n; i+=2) if(f[i]) res.push_back(i);
    return res;
}

int f(int x){
    if(x < 10)return x;
    else{
        int y = 0;
        while(x){
            y += x % 10;
            x /= 10;
        }
        return f(y);
    }
}

const int MA = 18000;
int sum[10][MA];

int main(){
    int K, N;
    cin >> K >> N;
    auto ps_ = sieve(N);
    vi ps;
    each(p, ps_)if(p >= K)ps.push_back(p);
    int np = sz(ps);
    vi hs(np);
    rep(i, np)hs[i] = f(ps[i]), sum[hs[i]][i + 1] = 1;
    rep(i, 10)rep(j, np)sum[i][j + 1] += sum[i][j];
    
    int ma = 0, val = -1;
    rep(l, np){
        int ok = l + 1, ng = np + 1, mid, len;
        while(ng - ok > 1){
            mid = (ok + ng) >> 1;
            bool a = true;
            rep(i, 10)a &= (sum[i][mid] - sum[i][l] <= 1);
            (a ? ok : ng) = mid;
        }
        len = ok - l;
        if(len >= ma){
            ma = len;
            val = ps[l];
        }
    }
    cout << val << endl;
}