#include<bits/stdc++.h>
using namespace std;
using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
template<class T> using V = vector<T>;
template<class T> using VV = V<V<T>>;
template<class T> using VVV = V<VV<T>>;
template<class T> using VVVV = VV<VV<T>>;
#define rep(i,n) for(ll i=0ll;i<n;i++)
#define REP(i,a,n) for(ll i=a;i<n;i++)
const long long INF = (1LL << 60);
const long long mod99 = 998244353;
const long long mod107 = 1000000007;
const long long mod = mod99;
#define eb emplace_back
#define pb eb
#define be(v) (v).begin(),(v).end()
#define all(i,v) for(auto& i : v)
#define all2(i,j,v) for(auto& [i,j] : v)
template<class T, class U> void chmin(T& t, const U& u) { if (t > u) t = u; }
template<class T, class U> void chmax(T& t, const U& u) { if (t < u) t = u; }

// cin.tie(nullptr);
// ios::sync_with_stdio(false);
// cout << fixed << setprecision(20);

void solve(){
  ll n,m;
  cin >> n >> m;
  V<ll> v(2001000, 1);
  v[0] = 0;
  v[1] = 0;
  REP(i,2,2001000) if(v[i]){
  	for(ll j=2*i;j<2001000;j+=i) v[j] = 0;
  	v[i] = i;
  	while(v[i] >= 10){
  		ll x = 0;
  		while(v[i]){
  			x += v[i]%10;
  			v[i] /= 10;
  		}
  		v[i] = x;
  	}
  }
  ll ans = 0, len = 0;
  ll cnt = 0;
  ll R=n;
  V<ll> h(10, 0);
  REP(L,n,m+1){
  	while(R<=m){
  		if(v[R]==0) R++;
  		else if(h[v[R]]) break;
  		else{
  			h[v[R]]++;
  			R++;
  			cnt++;
  		}
  	}
  	if(len<=cnt){
  		len = cnt;
  		ans = L;
  	}
  	h[v[L]]--;
  	if(v[L]>0) cnt--;
  }
  cout << ans << endl;
}





int main(){
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  int t=1;
  // cin >> t;
  rep(i,t) solve();
}