q = []
while true
  s = gets.chomp.split(",").map(&:to_i)
  if s == []
    break
  end
  q << s
end
n = q.length
sum = 0
for i in 2..n-1
  sum += ((q[i-1][0]-q[0][0])*(q[i][1]-q[0][1])-(q[i-1][1]-q[0][1])*(q[i][0]-q[0][0])).abs
end
puts sum