fn prime_count(n: usize) -> usize {
    if n <= 1 {
        return 0;
    }
    let sqrt = (1..).find(|p| p * p > n).unwrap() - 1;
    let mut large = vec![0; sqrt + 1];
    let mut small = vec![0; sqrt + 1];
    for (i, (large, small)) in large.iter_mut().zip(&mut small).enumerate().skip(1) {
        *large = n / i - 1;
        *small = i - 1;
    }
    for p in 2..=sqrt {
        if small[p] == small[p - 1] {
            continue;
        }
        let pi = small[p] - 1;
        let q = p * p;
        for i in 1..=sqrt.min(n / q) {
            large[i] -= *large.get(i * p).unwrap_or_else(|| &small[n / (i * p)]) - pi;
        }
        for i in (q..=sqrt).rev() {
            small[i] -= small[i / p] - pi;
        }
    }
    large[1]
}

fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    let a = s.trim().split_whitespace().flat_map(|s| s.parse::<usize>()).collect::<Vec<_>>();
    let (l, r) = (a[0], a[1]);
    let ans = prime_count(r) - prime_count(l - 1) + prime_count(2 * r) - prime_count(2 * l);
    println!("{}", ans);
}