import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class No0192 {
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		int N = Integer.parseInt(br.readLine());
		System.out.println( N % 2 == 0 ? N : N - 1);
	}
}