Each day at The Phone Company a batch job puts all the customer calls for the previous day into a single log file of:
'customer id','phone number called','call duration'
For a customer the cost of a call under 3 minutes is 0.05p/sec, over 3 minutes it is 0.03p/sec. However, there is a promotion on and the calls made to the phone number with the greatest total cost is removed from the customer's bill.
Write a program that when run will parse the calls.log file and print out the total cost of calls for the day for each customer. You can use any libraries you wish to.