We are working with “KETTLE”, we have a query

we working file. it has 21 records is there last record is footer. this 21th record. this file has one colum is
CUSTNUM. this footer is 20. means CUSTNUM=20.
my senario is CUSTNUM=number records then file is upload. otherwise not uploaded.

we have implemented
1.one flow is num of records count( it done)
2.second flow is i have found last record custnum=20( it aslo done)
how to calucate custnum=count -1;
major problem is it has no column to column maping. and not expreesion editor
is it possible? Please reply ASAP.