Untitled

import java.util.Scanner;

public class P1 {
	public static float Sol(int x, int n) {
		float sumValue = 1;
		int sumtmp = 1;

		for (int i = 2; i <= n; i++) {
			sumtmp += i;
			sumValue += 1.0 / (Math.pow(-1, i + 1) * sumtmp);
		}

		return sumValue;
	}

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int x = sc.nextInt();
		int n = sc.nextInt();

		System.out.println(Sol(x, n));
//		Sol(x, n);
//		if (Sol(n)) {
//			System.out.println("YES");
//		} else {
//			System.out.println("NO");
//		}
	}
}