#include <bits/stdc++.h>

typedef long long ll;
typedef unsigned long long ull;

#define FOR(i,a,b) for(int (i)=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define RANGE(vec) (vec).begin(),(vec).end()

using namespace std;

std::set<int> sieve(int n) {
        std::vector<bool> is_prime(n+1);
        fill(is_prime.begin(), is_prime.end(), true);
        is_prime[0] = is_prime[1] = false;
        for (int i = 2; i <= n; ++i)
        {
            if ( is_prime[i] )
            {
                for (int j = 2*i; j <= n; j += i)
                    is_prime[j] = false;
            }
        }
        std::set<int> ans;
        for (int i = 0; i < is_prime.size(); ++i)
        {
            if ( is_prime[i] )
                ans.insert(i);
        }
        return ans;
}
class UselessHash {
public:
    static int hash(int n) {
            int a = n/10;
            int b = n%10;
            if (a == 0)
                return b;
            return hash(b+hash(a));
    }
    void solve(void) {
            int K, N;
            cin>>K>>N;
            auto P = sieve(N);
            if (K > 1)
            {
                auto Q = sieve(K-1);
                for (auto q : Q)
                    P.erase(q);
            }
            vector<int> primes(RANGE(P));
            vector<int> val(primes);

            // hash 値に変換
            transform(RANGE(val), val.begin(), hash);
            int ans = 0;
            int idx = 0;
            int start = 0;
            map<int,int> cnt;

            // 0 初期化
            REP(i, val.size())
                cnt.insert(make_pair(val[i], 0));

            // しゃくとり法
            // O(2*log(n)*n)
            REP(i, val.size())
            {
                if (cnt[val[i]])
                {
                    while (start < val.size() && cnt[val[i]])
                    {
                        --cnt[val[start]];
                        ++start;
                    }
                }
                ++cnt[val[i]];
                int newlen = (i-start+1);
                if (ans <= newlen)
                {
                    ans = newlen;
                    idx = start;
                }
            }
            cout<<primes[idx]<<endl;
    }
};

#if 1
int main(int argc, char *argv[])
{
        ios::sync_with_stdio(false);
        auto obj = new UselessHash();
        obj->solve();
        delete obj;
        return 0;
}
#endif