/* -*- coding: utf-8 -*-
 *
 * 6.cc: No.6 使いものにならないハッシュ - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_P = 200000;

/* typedef */

typedef vector<int> vi;

/* global variables */

bool primes[MAX_P + 1], used[10];

/* subroutines */

void gen_primes(int maxp) {
  memset(primes, true, sizeof(primes));
  primes[0] = primes[1] = false;

  int p;
  for (p = 2; p * p <= maxp; p++)
    if (primes[p])
      for (int q = p * p; q <= maxp; q += p) primes[q] = false;
}

int calchash(int n) {
  while (n >= 10) {
    int sum = 0;
    while (n > 0) {
      sum += n % 10;
      n /= 10;
    }
    n = sum;
  }
  return n;
}

/* main */

int main() {
  int k, n;
  cin >> k >> n;

  gen_primes(n);

  vi pnums, hs;
  for (int p = k; p <= n; p++)
    if (primes[p]) pnums.push_back(p), hs.push_back(calchash(p));

  int hn = hs.size();
  //for (int i = 0; i < hn; i++) printf(" %d", hs[i]); putchar('\n');

  int maxd = 0, minp = -1;
  for (int i = 0, j = 0; j < hn; i++) {
    while (j < hn && ! used[hs[j]]) used[hs[j++]] = true;
    int d = j - i;
    if (maxd <= d) maxd = d, minp = pnums[i];
    used[hs[i]] = false;
  }

  printf("%d\n", minp);
  return 0;
}