#include <iostream> 
#include <string> 
#include <vector> 
#include <cmath> 
#include <algorithm> 
#include <cstdlib> 
#include <ctime> 
#include <cstdio> 
#include <functional> 
#include <set> 
#include <sstream> 
#include <cctype>

using namespace std; 


int main(){

	int n,k;
	cin>>n>>k;
	
	srand(time(NULL));

	long win=0;
	for(long i=0;i<(2<<20);i++){
		int jiro=0,taro=0;
		for(int j=0;j<n;j++) jiro+=(rand()%6+1);
		for(int j=0;j<n-k;j++) taro+=(rand()%6+1);
		for(int j=0;j<k;j++) taro+=(rand()%3+4);

		if(taro>jiro) win++;
	}

	printf("%.16f\n",(double)win/(2<<20));

	return 0;
}