Assembly code output

R1,R2,R3 are registers

START : POP R1
POP R2
COMPARE R2,0
JUMP_EQ DONE_Z
PUSH R2
PUSH R1
SUBTRACT R2,1
PUSH R2
CALL START
POP R3
POP R1
POP R2
MULTIPLY R3,R2
JUMP DONE
DONE_Z:MOVE R3,1
DONE:PUSH R3
PUSH R1
RETURN

What can be the result of this code