Sumif / lookup for a value and sum

Hi

Column A has employee Numbers . ( May repeat , not necessarily specific no.of times )
Column B has date of Joining
Column C has effective date ( There is certain amount to be paid to that employee , from that date until it is revised to a new value )
Column D to - Column H has Months .(Jan-2013 to Jun 2013 ) with the amount to be paid as stated above.

Can anyone please help me with the total amount to be paid for an employee considering the updated values .

As shown in the excel , coloured cells are to be summed up for an employee (ex:- Emp.No 1 , Emp. No 2 )


Emp. No Date of Joining Effective Date Jan-13 Feb-13 Mar-13 Apr-13 May-13 Jun-13
1 1-Dec-12 1-Dec-12 1001 10000 4000 1000 3000 500
2 1-Jan-13 1-Jan-13 1021 12100 4840 1210 3630 605
1 1-Dec-12 1-Apr-13 0 0 0 1000 3993 666
3 2-Feb-13 1-Feb-13 0 14641 5856 1464 4392 732
1 1-Dec-12 1-May-13 0 0 0 0 5315 886
4 3-Jun-13 1-Jun-13 0 0 0 0 0 974
5 5-Mar-13 1-Apr-13 0 0 0 2358 7074 1179
2 1-Jan-13 1-Mar-13 0 0 11412 2853 8559 1427
2 1-Jan-13 1-Apr-13 0 0 0 1100 3300 550

Emp.No Jan-13 Feb-13 Mar-13 Apr-13 May-13 Jun-13
1
2
3
4
5

regret , if I m unable to explain the scenario , please refer to the attachment.

Regards
Sri.