while line = gets
    a, l, x = line.chomp.split.map(&:to_i)
    h = Math.sqrt(l ** 2 - (a ** 2 / 4.0))
    result = a * h / 2
    s = (l + l + x) / 2.0
    result += 2 * Math.sqrt(s * (s - l) *(s - ((l + x) / 2.0)) * (s - ((l + x) / 2.0)))
    puts result
end

