3 way join component

Hi, I have 3 files each having 2 cols e.g File1 empid deptid 1 100 2 200 3 200 4 100 5 300 File2 empid salary 1 10 2 20 3 30 4 40 5 50 6 60 File3 deptid deptname 100 A 200 B 300 C 400 D in the output i want total amt spent on each dept i.e A,B,C,D which would be a sum in rollup for each dept(100,200,300,400) salary of each employee. So here i will have to join File1.empid =File2.empid (which gives salaries) AND File1.deptid = File3.deptid (which gives dept name) So... in o/p i want dept_name and amt_spent_each_dept My solution has File1 --- File2 ------[ JOIN] ---[Rollup] --- [File4 as output] File3 --- But what condition can i have in JOIN component to join these 3 tables ? Please help its urgent