def aop()
  i = 0
  b = []
  a =[]
  c = []
  while c = gets
    b = c.split(',').map(&:to_f)
    puts b
    a[i] = b
    i += 1
  end
  t = 0
  for i in 1..a.length-2
    x = ((a[0][0]-a[i][0])**2 + (a[0][1]-a[i][1])**2)**(1/2.0)
    y = ((a[0][0]-a[i+1][0])**2 + (a[0][1]-a[i+1][1])**2)**(1/2.0)
    z = ((a[i+1][0]-a[i][0])**2 + (a[i+1][1]-a[i][1])**2)**(1/2.0)
    w = (x + y + z)/2.0
    s = (w*(w-x)*(w-y)*(w-z))**(1/2.0)
    t += s
  end
  puts t
end

aop()