n = read_line.to_i
dp = Array.new(n) { Array.new(6, 0.0) }
dp[0][0] = 1
n.pred.times do |i|
	6.times do |j|
		dp[i + 1][j] += dp[i][j] * (j.succ.to_f / 6)
		dp[i + 1][j + 1] += dp[i][j] * (1 - j.succ.to_f / 6) if j != 5
	end
end
puts dp[n - 1][5]