#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <iomanip>
#include <assert.h>
#include <array>
#include <cstdio>

//#define int ll

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

typedef long long ll;

bool pr[200001];
int PSIZE;
int vpr[200001];
int phash[200001];

int memo[200001];

int get_hash(int x) {
  if(memo[x] > 0) { return memo[x]; }
  if(x < 10) { return x; }
  string s = to_string(x);
  int sum = 0;
  int size = s.size();
  rep(i, size) {
    sum += s[i]-'0';
  }
  return memo[x] = get_hash(sum);
}

signed main() {

  int K, N; cin >> K >> N;

  fill(pr, pr+200001, 1);

  pr[0] = pr[1] = 0;
  for(int i=2; (ll)i*i <= N+1; i++) {
    if(pr[i]) {
      for(ll j=i*i; j<=N+1; j+=i) {
        pr[j] = 0;
      }
    }
  }
  for(int i=K; i<=N+1; i++) {
    if(pr[i]) vpr[PSIZE++] = i;
  }

  rep(i, PSIZE) {
    phash[i] = get_hash(vpr[i]);
  }

  int maxlen = 0, ans = 0;
  int l = 0, r = 0;

  unordered_set<int> st;
  while(1) {
    if(r >= PSIZE) { break; }
    if(!st.count(phash[r])) {
      st.insert(phash[r]);
      if(maxlen <= (int)st.size()) {
        maxlen = st.size();
        ans = vpr[l];
      }
      r++;
    }
    else {
      while(1) {
        st.erase(phash[l++]);
        if(l == r) { break; }
        if(!st.count(phash[r])) {
          break;
        }
      }
    }
  }

  cout << ans << endl;

  return 0;
}