n, m = gets.split.map &:to_i
r = gets.to_f

n, m = m, n if m == 1

puts(
  case
  when [n, m] == [1, 1] then r
  when n == 1 then 2 * r**2 + (m - 2) * r**3
  else 4 * r**3 + 2*(n + m - 4) * r**4 + (n - 2) * (m - 2) * r**5
  end
)