//
//  main.swift
//  AtCoder
//
//  Created on 2019/03/22.
//  Copyright © 2019 yutake2000. All rights reserved.
//

import Foundation

class Scanner {
    var buffer: [String.SubSequence]
    func next() -> String {
        if (buffer.count == 0) {
            if let line = readLine() {
                buffer = line.split(separator: " ")
            }
        }
        return (buffer.count == 0) ? "" : String(buffer.removeFirst())
    }
    func nextInt() -> Int {
        return Int(next())!
    }
    func nextDouble() -> Double {
        return Double(next())!
    }
    init() {
        buffer = []
    }
}

var sc = Scanner()

var K = Int(sc.next())!

if K % 2 == 0 {
    print(K * K / 4)
} else {
    print((K+1) * (K-1) / 4)
}