def cos(a, b, c)
	(a * a + b * b - c * c).to_f / (2 * a * b)
end

def calc(a, b, c)
	a = a.to_f / 2
	b = b.to_f / 2
	Math.sqrt(a * a + b * b - 2 * a * b * cos(a * 2, b * 2, c))
end

def tri(a, b, c)
	s = (a + b + c).to_f / 2
	Math.sqrt(s * (s - a) * (s - b) * (s - c))
end

a, b, c = gets.split.map(&:to_i)
puts tri(calc(a, b, c), calc(a, c, b), calc(b, c, a))