import java.util.Scanner;

public class Tester2 {

	private static final int MAX = 1000000000;
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		if(1<=n && n<=MAX)
			System.out.println(chk(n));
	}

	static int chk(int n) {
		double a = n*1.5;
		int m = (int)a/1;
		return m;
	}
}