local function printd(v)
  print(string.format("%.10f", v))
end
local n, m = io.read("*n", "*n")
local p = io.read("*n")
if m < n then n, m = m, n end
if m == 1 then
  printd(p)
elseif n == 1 then
  printd(p * p * 2 + p * p * p * (m - 2))
else
  local ret = p * p * p * 4
  ret = ret + ((n - 2) * 2 + (m - 2) * 2) * p * p * p * p
  ret = ret + (n - 2) * (m - 2) * p * p * p * p * p
  printd(ret)
end