FUNCTION PBMAIN () AS LONG
    DIM m AS QUAD, n AS QUAD

    m = ABS(VAL(INPUTBOX$("Enter a whole number.")))
    n = ABS(VAL(INPUTBOX$("Enter another whole number.")))

    MSGBOX STR$(Ackermann(m, n))
END FUNCTION

FUNCTION Ackermann (m AS QUAD, n AS QUAD) AS QUAD
    IF 0 = m THEN
        FUNCTION = n + 1
    ELSEIF 0 = n THEN
        FUNCTION = Ackermann(m - 1, 1)
    ELSE    ' m > 0; n > 0
        FUNCTION = Ackermann(m - 1, Ackermann(m, n - 1))
    END IF
END FUNCTION