fn eratosthenes(n: usize) -> Vec<bool> {
    let mut isprime = vec![true; n + 1];
    isprime[0] = false;
    isprime[1] = false;

    for i in 2..=n {
        if !isprime[i] { continue; }
        for j in 2..=n / i {
            isprime[j * i] = false;
        } 
    }
    isprime
}

fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();

    let prime = eratosthenes(n);

    let mut ans = 0;
    for i in 0..prime.iter().count() {
        if prime[i] { ans += i; }
    }
    println!("{}", ans);
}