import java.util.Random;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int N = scanner.nextInt();
		int K = scanner.nextInt();

		Random r = new Random();
		int win = 0;
		int lose = 0;
		long iteration = 5000000L;
		for (int i = 0; i < iteration; i++) {
			int jiro = 0;
			for (int j = 0; j < N; j++) {
				jiro += r.nextInt(6) + 1;
			}
			int taro = 0;
			for (int j = 0; j < N - K; j++) {
				taro += r.nextInt(6) + 1;
			}
			for (int j = 0; j < K; j++) {
				taro += r.nextInt(3) + 4;
			}
			if (jiro < taro)
				win++;
		}

		System.out.format("%f", ((float) win) / iteration);

	}

}