fn get_primes(n: usize) -> Vec<bool> {
    let mut flgs: Vec<bool> = vec![true; n+1];
    flgs[0] = false;
    flgs[1] = false;
    for i in 0..=((n as f64 + 1.0).sqrt().floor() as usize) {
        if !flgs[i] { continue; }
        for j in i..=n/i {
            flgs[j*i] = false;
        }
    }
    flgs
}

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

    println!("{}", get_primes(n).iter().enumerate().filter(|pair| *pair.1).map(|pair| pair.0).sum::<usize>());
}