import std.algorithm, std.array, std.container, std.range;
import std.string, std.conv, std.math, std.random;
import std.stdio, std.typecons;

alias Tuple!(int, "x", int, "y") point;

void main()
{
  auto n = readln.chomp.to!int;
  auto k = readln.chomp.to!int;

  const a = 2000000;
  auto r = 0;

  foreach (i; 0..a) {
    auto t1 = iota(k).map!(j => uniform(4, 7)).sum;
    auto t2 = iota(n - k).map!(j => uniform(1, 7)).sum;
    auto ji = iota(n).map!(j => uniform(1, 7)).sum;
    if (t1 + t2 > ji)
      r += 1;
  }

  writefln("%f", r.to!real / a);
}