public static void main(String[] args) throws IOException {
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		String line = "";
		StringBuilder out = new StringBuilder();
		while ((line = in.readLine()) != null && line.length() != 0) {
			int n = Integer.parseInt(line.trim());
			out.append((n % 2 == 0 ? n + n / 2 : n + (n - 1) / 2) + "\n");
		}
		System.out.print(out);
	}