struct FenwickTree {
    val: Vec<usize>,
}

impl FenwickTree {
    fn new(n: usize) -> Self {
        FenwickTree {
            val: vec![0; n + 1],
        }
    }
    fn add(&mut self, mut x: usize, v: usize) {
        while let Some(p) = self.val.get_mut(x) {
            *p = p.wrapping_add(v);
            x += x & (!x + 1);
        }
    }
    fn sum(&mut self, mut x: usize) -> usize {
        assert!(x < self.val.len());
        let mut ans = 0usize;
        while x > 0 {
            ans = ans.wrapping_add(self.val[x]);
            x -= x & (!x + 1);
        }
        ans
    }
}

// N 以下の素数を列挙
fn sieve(n: usize) -> Vec<usize> {
    let mut is_prime = vec![true; n + 1];
    for i in 2.. {
        if i * i > n {
            break;
        }
        if is_prime[i] {
            let mut j = i * i;
            while j <= n {
                is_prime[j] = false;
                j += i;
            }
        }
    }
    let len = is_prime.iter().skip(2).filter(|p| **p).count();
    let mut prime = Vec::with_capacity(len);
    for (i, is_prime) in is_prime.into_iter().enumerate().skip(2) {
        if is_prime {
            prime.push(i);
        }
    }
    prime
}

// N 以下の素数の個数を数える
fn prime_count(n: usize) -> usize {
    if n <= 1 {
        return 0;
    }
    let mut m = 1;
    while (m + 1) * (m + 1) <= n {
        m += 1;
    }
    let prime = sieve(m);
    let bound = (n as f64 / (n as f64 + 10.0).log10()).cbrt().powi(2) as usize + 1;
    let batch = (n as f64).sqrt() as usize + 1;
    let mut ans = prime.len() - 1;
    let mut query = vec![vec![]; bound / batch + 1];
    let mut stack = vec![(n, prime.len(), 1usize)];
    while let Some((n, k, sign)) = stack.pop() {
        if k == 0 {
            ans = ans.wrapping_add(sign.wrapping_mul(n));
            continue;
        }
        let p = prime[k - 1];
        if p * p > n {
            let x = match prime[..k].binary_search_by(|p| p.pow(2).cmp(&n)) {
                Ok(k) => k + 1,
                Err(k) => k,
            };
            ans = ans.wrapping_sub(sign.wrapping_mul(k - x));
            stack.push((n, x, sign));
        } else if n <= bound {
            query[n / batch].push((n, k, sign));
        } else {
            stack.push((n, k - 1, sign));
            stack.push((n / p, k - 1, !sign + 1));
        }
    }
    let mut sum = vec![0; prime.len()];
    for (i, mut query) in query.into_iter().enumerate() {
        query.sort_by_key(|p| !p.1);
        let left = i * batch;
        let right = (i + 1) * batch;
        let mut is_prime = vec![true; batch];
        let mut bit = FenwickTree::new(batch);
        for i in 1..=batch {
            bit.add(i, 1);
        }
        for (i, &p) in prime.iter().enumerate() {
            if p >= right {
                break;
            }
            let mut k = (left + p - 1) / p * p;
            while k < right {
                let x = k - left;
                if is_prime[x] {
                    is_prime[x] = false;
                    bit.add(x + 1, !0);
                }
                k += p;
            }
            while let Some(&(n, k, sign)) = query.last() {
                if k == i + 1 {
                    let x = n - left;
                    ans = ans.wrapping_add(sign.wrapping_mul(sum[i] + bit.sum(x + 1)));
                    query.pop();
                } else {
                    break;
                }
            }
            sum[i] += bit.sum(batch);
        }
    }
    ans
}

// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------

fn run() {
    input!(l: usize, r: usize);
    let mut ans = 0;
    ans += prime_count(r);
    ans -= prime_count(l - 1);
    if r - l >= 1 {
        ans += prime_count(2 * r - 1);
        ans -= prime_count(2 * l);
    }
    println!("{}", ans);
}

fn main() {
    run();
}