#include<cstdio>
#include<cstring>
#include<iostream>
#include<cmath>
#include<string>
#include<algorithm>
#include<vector>
#include<queue>
#include<map>
using namespace std;
typedef long long LL;
const int M=1e6+10;
const LL MOD=1e9+7;

bool is_p[M];
int prime[M];
LL sqrtn;

int euler(int N) {
    int len = 0;
    memset(is_p, true, sizeof(is_p));
    for(int i = 2; i < N; i++) {
        if(is_p[i]) {
            len++;
            prime[len] = i;
        }
        for(int j = 1; j <= len && prime[j] <= i; j++) {
            if(i * prime[j] >= N) {
                break;
            }
            is_p[i * prime[j]] = false;
            if(i % prime[j] == 0) {
               
                break;
            } else {

            }
        }
    }
    return len;
}


LL L[M],R[M];
LL primepi(LL n){
    if(n<2) return 0;
    for(LL i=1;i<=sqrtn;++i)   R[i]=n/i-1;
    for(LL i=1;i<=sqrtn;++i)   L[i]=i-1;
    for(int s=1;prime[s]<=sqrtn;s++){
        LL ps=prime[s];
        for(LL i=1,tn=min(n/(ps*ps),sqrtn);i<=tn;++i){
            R[i] -= (i*ps<=sqrtn?R[i*ps]:L[n/(i*ps)])-L[ps-1];
        }
        for(LL i=sqrtn;i>=ps*ps;--i){
            L[i] -= L[i/ps]-L[ps-1];
        }
    }
    return R[1];
}


int main(){
    LL l,r;
    scanf("%lld%lld",&l,&r);
    sqrtn=ceil(sqrt(2*r));
    euler(sqrtn*2);
    LL ans1 = primepi(r)-primepi(l-1);
    LL ans2 = l==r?0:primepi(2*r-1)-primepi(2*l);
    printf("%lld\n",ans1+ans2);
    return 0;
}