Shifts and Roster Staff

 Hi

I have 3 shifts, and we also have a 4 roster staff for that shift. for example.. 

Shifts

A 08:00 - 16:00

B 16:00 - 00:00

C  00:00 - 08:00

Rosters

R1

R2

R3

R4

for example: 

On Mon  R1 attend Shift A, R2 attend Shift B and R3 attend shift C.

On Tue   R4 attend Shift A, R1 attend Shift B and R2 attend shift C.

On Wed  R3 attend Shift A, R4 attend Shift B and R1 attend shift C.

On Thu   R2 attend Shift A, R3 attend Shift B and R4 attend shift C.

On Fri     R1 attend Shift A, R2 attend Shift B and R3 attend shift C.