use std::io::*;
use std::str::FromStr;
use utils::*;

pub fn main() {
    let i = stdin();
    let mut o = Vec::new();
    run(i.lock(), &mut o);
    stdout().write_all(&o).unwrap();
}

fn run<R: BufRead, W: Write>(i: R, o: &mut W) {
    let mut i = ReadEx::from(i);
    let n = i.read::<f64>();
    writeln!(o, "{}", n * 3.5).unwrap();
}

mod utils {
    use super::*;

    pub struct ReadEx<R: BufRead> {
        r: R,
        s: String,
    }

    impl<R: BufRead> ReadEx<R> {
        pub fn from(r: R) -> Self {
            ReadEx {
                r: r,
                s: String::new(),
            }
        }
        pub fn read_line(&mut self) -> &str {
            self.s.clear();
            self.r.read_line(&mut self.s).unwrap();
            self.s.trim()
        }

        pub fn read<T: FromStr>(&mut self) -> T {
            self.read_line().parse().ok().unwrap()
        }
    }
}