fn main() {
    let stdin = std::io::read_to_string(std::io::stdin()).unwrap();
    let mut stdin = stdin.split_ascii_whitespace();

    let n: u32 = stdin.next().unwrap().parse().unwrap();

    println!("{}", output(solve(n)));
}

fn solve(n: u32) -> u32 {
    n * 3 / 2
}

fn output(ans: u32) -> u32 {
    ans
}