use std::io::{stdin, Read};

fn main() {
    let mut buf = String::new();
    stdin().read_to_string(&mut buf).unwrap();
    let mut tok = buf.split_whitespace();
    let mut get = || tok.next().unwrap();
    macro_rules! get {
        ($t:ty) => (get().parse::<$t>().unwrap());
        () => (get!(usize));
    }
    
    let n = get!();
    
    let mut xs = vec![false; n + 1];
    let mut ys = vec![];
    for i in 2..xs.len() {
        if xs[i] { continue; }
        ys.push(i);
        for j in 2..xs.len() {
            if i * j >= xs.len() { break; }
            xs[i*j] = true;
        }
    }
    let mut ans: usize = ys.iter().sum();
    if let Some(s) = ys.iter().filter(|&y| y * 2 <= n).last() {
        ans += s;
    }
    println!("{}", ans - 2);
}