use std::io;

fn main() {
    let mut s = String::new();
    io::stdin().read_line(&mut s).unwrap();
    let n: u64 = s.trim().parse().unwrap();
    let r = ((n as f64)/3.).sqrt() as u64;
    assert!({
        let n_ = 3 * r * r;
        if n > n_ { n - n_ <= 1000000 }
        else { n_ - n <= 1000000 }
    });
    println!("{}", r);
}