import std.algorithm, std.array, std.container, std.range, std.bitmanip;
import std.numeric, std.math, std.bigint, std.random, core.bitop;
import std.string, std.regex, std.conv, std.stdio, std.typecons;

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

  real calc(real pseudo) {
    auto pi = new real[](k + 6);
    pi[k] = 0;
    pi[k + 1..k + 6] = pseudo;

    foreach_reverse (i; 0..k)
      pi[i] = (pi[i + 1..i + 7].sum) / 6 + 1;

    return pi[0];
  }

  auto p = 0.001;
  while (calc(p) > p) p *= 2;

  auto r = iota(p / 2, p, 0.001).assumeSorted!((a, _) => calc(a) >= a).lowerBound(0);
  writefln("%.3f", r.back);
}