def area(a, b, c)
  z = (a + b + c) / 2
  return Math.sqrt(z * (z - a) * (z - b) * (z - c))  
end

def edge(p1x, p1y, p2x, p2y, p3x, p3y)
  a = dist(p1x, p1y, p2x, p2y)
  b = dist(p2x, p2y, p3x, p3y)
  c = dist(p3x, p3y, p1x, p1y)
  
  return [a, b, c]
end

def dist(x1, y1, x2, y2)
  return Math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2)
end

p, sum = [], 0

p << $_.split(",").map(&:to_f) while gets

(p.length - 2).times do |i|
  sum += area(*edge(*p[0], *p[i + 1], *p[i + 2]))
end

puts sum