We have thousand of customers while they have different
peak seasons. Some of them have more business in summer
and some of them have more business in winter. How to re-
assign these customers to CS staff so that their workload
will be more evenly, but not someone's very busy in summer
but idle in winter.

My raw data looks like following:
Customer A 12/15/2005 Staff A
Customer C 12/15/2005 Staff C
Customer A 12/15/2005 Staff A
Customer A 12/16/2005 Staff A
Customer B 12/16/2005 Staff B
Customer A 12/17/2005 Staff A
Customer A 12/17/2005 Staff A
Customer A 12/17/2005 Staff C