defmodule Main do
  def main do
    [a, b, n] =
      IO.gets("")
      |> String.trim()
      |> String.split()
      |> Enum.map(&String.to_integer/1)
    first = floor(a * n / b) - a * floor(n / b)
    #second = floor(a * (n - 1) / b) - a * floor((n - 1) / b)
    #third = floor(a * 2 / b) - a * floor(2 / b)
    last = floor(a / b) - a * floor(1 / b)
	IO.puts(max(first, last))
    #solve(a, b, n, floor(a * n / b) - a * floor(n/ b))
  end
end