#!/usr/bin/ruby
# coding: utf-8

PI = Math.acos(-1)

def sub(a, b)
  [a[0] - b[0], a[1] - b[1]]
end

def cross(a, b)
  a[1] * b[0] - a[0] * b[1]
end

def triangle(a, b, c)
  b = sub(b, a)
  c = sub(c, a)
  cross(b, c).abs / 2.0
end

ps = []
while true
  line = gets
  if line == nil
    break
  end
  p = line.chomp.split(',').map{|x| x.to_f}
  ps.push p
end

area = 0.0
for i in 1...ps.length-1
  area += triangle(ps[0], ps[i], ps[i+1])
end
puts area