import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int K = sc.nextInt();
    double win = 0;
    for(int i = 0; i < 1000000; i++) {
      int p1 = 0;
      int p2 = 0;
      Random rnd = new Random();
      for(int j = 0; j < N; j++) {
        p1 += (rnd.nextInt(6) + 1);
      }
      for(int j = 0; j < K; j++) {
        p2 += (rnd.nextInt(3) + 4);
      }
      for(int j = 0; j < N - K; j++) {
        p2 += (rnd.nextInt(6) + 1);
      }
      if(p2 > p1) win++;
    }
    System.out.println(win / (double)1000000);
  }
}