require "matrix"

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

def tri(p1, p2, p3)
  edge = []
  edge << Vector[p1[0] - p2[0], p1[1] - p2[1]].r
  edge << Vector[p2[0] - p3[0], p2[1] - p3[1]].r
  edge << Vector[p3[0] - p1[0], p3[1] - p1[1]].r
  
  return edge
end

arr, sum = [], 0

while line = gets
  arr << line.split(",").map(&:to_i)
end

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

puts sum