#![allow(non_snake_case)]

use std::cmp;
use std::io::{ self, prelude::* };

macro_rules! pick {
    ($tokens:expr) => {
        $tokens.next().unwrap().parse().expect("parse error")
    }
}

fn f(N: i64, b: i64) -> i64 {
    (N-b)*(b+1) + b
}

fn main() {
    let mut s = String::new();
    io::stdin().read_to_string(&mut s).expect("i/o error");
    let mut tokens = s.split_whitespace();

    let N: i64 = pick!(tokens);

    let ans = cmp::max(f(N,N/2), f(N,N/2+1));

    println!("{}", ans);
}