#include <algorithm>
#include <iostream>
#include <cstdio>
#include <queue>
#include <vector>
#define task "SPRIME"

using namespace std;
using ll = unsigned long long;
using ld = long double;

const int N = 1e5 + 2;

ll l, r;
vector<ll> a;

void ReadInput()
{
    cin >> l >> r;
}

bool Check(ll v){
    if(v < 2)
        return 0;
    if(v % 2 == 0)
        return v == 2;
    for(ll i = 3; i * i <= v; i += 2)
        if(v % i == 0)
            return false;
    return true;
}

ll Pow(ll v){
    ll ans = 1;
    while(v){
        ans *= 10ll;
        v /= 10ll;
    }
    return ans;
}

ll make(ll c, ll i){
    return i * Pow(c) + c;
}

void Gen(){
    queue<ll> s;
    s.push(2); a.push_back(2);
    s.push(3); a.push_back(3);
    s.push(5); a.push_back(5);
    s.push(7); a.push_back(7);
    while(s.size()){
        ll c = s.front();
        s.pop();
        for(int i = 1; i < 10; ++i){
            ll  v = make(c, i);
            if(v <= r && Check(v)){
                s.push(v);
                a.push_back(v);
            }
        }
    }
}

void trau(){
    int cnt = 0;
    ll ls = l;
    while(l <= r){
        ll c = Pow(l) / 10, v = l;
        while(v){
            if(!Check(v))
                goto ABCDEF;
            v %= c;
            c /= 10;
            if(v < c)
                goto ABCDEF;
        }
        ++cnt;
        // << l << " ";
        ABCDEF:;
        ++l;
    }
    l = ls;
    cout << "\n" << cnt << "\n";
}

void Solve()
{
    Gen();
    sort(a.begin(), a.end());
    //trau();
    //for(auto i : a)
    //    cout << i << " ";
    //cout << "\n";
    cout << (upper_bound(a.begin(), a.end(), r) - lower_bound(a.begin(), a.end(), l) );
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    if(fopen(task".INP", "r"))
        freopen(task".INP", "r", stdin),
        freopen(task".OUT", "w", stdout);
    ReadInput();
    Solve();
}