import java.util.*;

public class Main {
	
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		Random rnd = new Random();
		int n=sc.nextInt();
		int k=sc.nextInt();
		double v=0;
		for(int i=0;i<5000000;i++){
			int sumt=0;
			int sumj=0;
			for(int j=0;j<n;j++){
				if(j<k)sumt+=rnd.nextInt(3)+4;
				else sumt+=rnd.nextInt(6)+1;
				sumj+=rnd.nextInt(6)+1;
			}
			if(sumt>sumj)v++;
			
		}
		System.out.println(v/5000000);
		
		}
}