Oops.. I forgot to put the two files used.

Customer.txt

200207:ABC
200905:DEF
200403:GHI
200010:JKL


20100310.bill

200207 200207 SWITCH FastEthernet1_0_1 OUT 01-Feb-2010_02:00 01-Mar-2010_02:00 428.706 129.641
200207 200207 SWITCH FastEthernet1_0_1 IN 01-Feb-2010_02:00 01-Mar-2010_02:00 168.476 50.947
200207 200207 SWITCH FastEthernet1_0_2 OUT 01-Feb-2010_02:00 01-Mar-2010_02:00 65.223 19.723
200207 200207 SWITCH FastEthernet1_0_2 IN 01-Feb-2010_02:00 01-Mar-2010_02:00 37.958 11.478
200905 200905 SWITCH FastEthernet1_0_4 OUT 01-Feb-2010_02:00 01-Mar-2010_02:00 3.193 0.965
200905 200905 SWITCH FastEthernet1_0_4 IN 01-Feb-2010_02:00 01-Mar-2010_02:00 41.499 12.549
200403 200403 SWITCH FastEthernet1_0_5 OUT 01-Feb-2010_02:00 01-Mar-2010_02:00 1.396 0.422
200403 200403 SWITCH FastEthernet1_0_5 IN 01-Feb-2010_02:00 01-Mar-2010_02:00 38.862 11.752
200010 200010 SWITCH FastEthernet1_0_6 OUT 01-Feb-2010_02:00 01-Mar-2010_02:00 3.386 1.024
200010 200010 SWITCH FastEthernet1_0_6 IN 01-Feb-2010_02:00 01-Mar-2010_02:00 4.489 1.358