#include <bits/stdc++.h>
#define ll long long
#define pb push_back

#define task "SPRIME"

using namespace std;

ll Pow(ll x, ll mu, ll mod)
{
    if(mu == 0) return 1%mod;
    if(mu == 1) return x%mod;
    ll t = Pow(x, mu/2, mod)%mod;
    if(mu%2 == 0) return (t%mod*t%mod)%mod;
    else return ((t%mod*t%mod)%mod*x%mod)%mod;
}

bool miler(ll d, ll n, ll a)
{
    ll t = Pow(a, d, n);
    if(t == 1 || t == n-1) return true;
    while(d != n-1){
        t = (t*t)%n;
        d *= 2;
        if(t == 1) return false;
        if(t == n-1) return true;
    }
    return false;
}

bool chk(ll n)
{
    if(n <= 1 || n == 4) return false;
    if(n <= 3 || n == 7 || n == 61) return true;
    if(n%2 == 0) return false;
    ll d = n-1;
    while(d % 2 == 0){
        d/=2;
    }
    if(miler(d, n, 2) && miler(d, n, 7) && miler(d, n, 61) && miler(d, n, 3)){
        return true;
    }
    return false;

}

int main()
{
    if(fopen(task".INP", "r")){
        freopen(task".INP", "r", stdin);
        freopen(task".OUT", "w", stdout);
    }
    ll L, R;
    cin >> L >> R;
    ll ans = 0;
    ll p = 1;
    vector<ll>a;
    a.pb(0);
    while(a.size() != 0){
        vector<ll>b;
        for(ll x : a){
            for(int i=1; i<=9; i++){
                ll cur = i*p + x;
                //cout << cur <<"\n";
                if(cur <= R && chk(cur)){
                    b.pb(cur);
                    if(cur >= L){
                        ans ++;
                        //cout << cur <<" ";
                    }
                }
            }
        }
        a.swap(b);
        p *= 10;
    }
    cout << ans;
}