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 k = readln.chomp.to!int;

  auto dp = new double[k + 6];
  dp[k..(k + 6)] = 0;

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

  writefln("%f", dp[0]);
}