import java.util.Scanner;

public class Yukicoder58 {

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

		int taro = 0, jiro = 0;
		int taroWin = 0;

		for (int i = 0; i < 2000000; i++) {
			taro = 0;
			jiro = 0;
			for (int j = 0; j < N; j++) {
				taro += j < K ? (int) (Math.random() * 3 + 4) : (int) (Math.random() * 6 + 1);
				jiro += (int) (Math.random() * 6 + 1);
			}
			if (taro > jiro) taroWin++;
		}
		System.out.println(taroWin / 2000000.0);

	}
}