/*          J  A  I   S  H  R  E  E   R  A  M          */



#include <bits/stdc++.h>
using namespace std;

#ifdef LUCTIVUD
#include <buggyBaby.hpp>
pretty:: PrettyPrinter NonIterable;
#define cerr cout
#else
#define _____error_____(...)
#endif

#pragma GCC optimize("O3,unroll-loops,trapv")
#pragma GCC target("avx,avx2,fma,sse,sse2,sse3,sse4,popcnt,lzcnt")
// #pragma GCC optimize "trapv"






/*  Snips   */


typedef long long lld; typedef unsigned long long llu;

#define  forn(I7, E4) for(lld I7=0ll; I7 < E4; (I7)+=1ll)
#define forn1(I7, E4) for(lld I7=1ll; I7 < E4+1; (I7)+=1ll)
#define        len(v) ((int)((v).size()))
#define        all(x) (x).begin(), (x).end()
#define       rall(x) (x).rbegin(), (x).rend()
#define            f1 first
#define            s2 second



/*  Utils   */


const lld MOD = int(1e9) + 7;
const lld &mod = MOD;

const long double EPS = 1e-6;

const lld inf = 2e18;


struct custom_hash {
    static uint64_t splitmix64(uint64_t x) {
        // http://xorshift.di.unimi.it/splitmix64.c
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};



signed pleaseAC(void) {

#ifdef LUCTIVUD
    // auto end_time = std::chrono::high_resolution_clock::now();
    // std::chrono::duration<double> diff = end_time - start_time;
    // cerr << "Finished in : " << diff.count() << "\n";
#endif

    return 0;
}


void IAmJustice(void) {

    ios_base::sync_with_stdio(false); cin.tie(0);
    cout.precision(10); cout << fixed;

#ifdef LUCTIVUD
    // const auto start_time = std::chrono::high_resolution_clock::now();
    freopen("/home/luctivud/CPPractice/IO/Zinput.txt", "r", stdin);
    freopen("/home/luctivud/CPPractice/IO/Zoutput.txt", "w", stdout);
#endif

    return;
}








/* This part should be outside the main in global paradigm. */

const long long MAXN = (lld)(1e7) + 1ll; // MAXN Size

vector<long long >isPrime(MAXN , true); // checkIfPrime
vector<long long >prime_numbers; // List of prime numbers
vector<long long >smallest_prime_factor(MAXN); // smallest_prime_factor of a number


void manipulated_seive() {
    isPrime[0] = isPrime[1] = false ;
    
    prime_numbers.push_back(2);
    smallest_prime_factor[2] = 2ll;

    for (long long int i=4; i < MAXN ; i+=2) {
        isPrime[i] = false;
        smallest_prime_factor[i] = 2ll;
    }

    for (long long int i = 3; i < MAXN ; i+=2) {
        if (isPrime[i]) {
            prime_numbers.push_back(i);
            smallest_prime_factor[i] = i;
        }

        for (long long int j = 0; j < (int)prime_numbers.size() && i * prime_numbers[j] < MAXN && prime_numbers[j] <= smallest_prime_factor[i]; j++) {
            isPrime[i * prime_numbers[j]] = false;
            smallest_prime_factor[i * prime_numbers[j]] = prime_numbers[j] ;
        }
    }
}


/* This should be called inside main. */
    










/*:::::::::::::::::::::: LOGIC :::::::::::::::::::::::::*/





void solveEachTest(int _TestCase) {
    // cout << "Case #" << _TestCase << ": ";
    lld a, b; cin >> a >> b;

    lld ans = 0ll;
    for (lld i = a; i <= b; i++) {
        for (lld j = i; j <= b; j++) {
            if (abs(i - j) > 2) break;
            lld num = ((j * (j + 1)) - (i * (i - 1))) / 2;
            if (isPrime[num]) {
                ans += 1;
            }
        }
    }

    cout << ans;

    return;
}



/*:::::::::::::::::::::/LOGIC:::::::::::::::::::::::::*/


signed main() {

    IAmJustice();
    manipulated_seive();
    int _T0T4 = 1;
    // cin >> _T0T4;

    for (int _TestCase = 1; _TestCase <= _T0T4; _TestCase++) {
        solveEachTest(_TestCase);
        cout << "\n";
    }

    return pleaseAC();
}




/*  ~~
    .?.?.?.
*/