def area(p)
  x, y = p[0]
  s = 0.0
  oldV = [p[1][0]-x, p[1][1]-y]
  p[2..-1].each do |x1, y1|
    va = [x1-x, y1-y]
    s += triangleArea(va, oldV)
    oldV = va
  end
  s
end

def triangleArea(a, b)
  (a[0] * b[1] - a[1] * b[0])/2.0
end

if __FILE__ == $0
  points = []
  loop do
    input = gets
    break if input.nil?
    points << input.split(',').map(&:to_f)
  end
  p area(points)
end