#include <bits/stdc++.h>

template<typename T> T in() { abort(); return T(); }
template<> std::string in() { std::string str; std::cin >> str; return str; }
template<> int in() { int x; scanf("%d", &x); return x; }

template<typename T> void out(T x) { abort(); }
template<> void out(const char* x) { printf("%s\n", x); }
template<> void out(std::string x) { std::cout << x << std::endl; }
template<> void out(int x) { printf("%d\n", x); }
template<> void out(long x) { printf("%ld\n", x); }

bool isprime[212345];
void init() {
  for(int i = 0; i < 212345; ++i) {
    isprime[i] = true;
  }
  isprime[0] = isprime[1] = false;
  for(int i = 2; i < 1000; ++i) {
    if( not isprime[i] ) continue;
    for(int j = i * i; j < 212345; j+=i) {
      isprime[j] = false;
    }
  }
}

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

int main() {
  init();
  int x = in<int>();
  int y = in<int>();
  std::vector<int> primes;
  std::vector<int> cod;
  for(int i = x; i <= y; ++i) {
    if( not isprime[i] ) continue;
    primes.push_back(i);
    cod.push_back(f(i));
  }
  int res = 0;
  int max = 0;
  for(int i = 0; i < (int)primes.size(); ++i) {
    bool check[10] = {};
    int j;
    for(j = i;;++j) {
      if( j >= (int)primes.size() ) break;
      if( check[cod[j]] ) break;
      check[cod[j]] = true;
    }
    if( max <= j - i ) {
      max = j - i;
      res = primes[i];
    }
  }
  out(res);
  
  return 0;
}