fn main() {
	let mut s = String::new();
	std::io::stdin().read_line(&mut s).ok();
	let n: usize = s.trim().parse().unwrap();
	let mut l = vec![true; n + 1];
	let mut i = 2;
	while i * i <= n {
		let mut j = i;
		while i * j <= n {
			l[i * j] = false;
			j += 1;
		}
		i += 1;
	}
	println!("{}", (2..=n).filter(|&x| l[x]).sum::<usize>());
}