def main(input = STDIN)
  sum = 0
  first, second = input.gets.split(",").map(&:to_f), input.gets.split(",").map(&:to_f)
  while (cood = input.gets)
    cood = cood.split(",").map(&:to_f)
    sum += area(*first, *second, *cood)
    second = cood
  end
  puts sum
end
def area(x1, y1, x2, y2, x3, y3)
  a, b, c = e_distance(x1, y1, x2, y2), e_distance(x2, y2, x3, y3), e_distance(x3, y3, x1, y1)
  z = (a + b + c) / 2
  return (z * (z - a) * (z - b) * (z - c)) ** 0.5
end
def e_distance(x1, y1, x2, y2)
  return ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5
end
#File.open('data'){|f|main(f)}
# >> 2.499999999999999
main