f
(
n
)
=
a
f
(
n
-
b
f
(
n
-
c
)
)
:
a
3
b
1
c
1
r
a
n
g
e
o
f
n
3
0
i
n
d
i
r
e
c
t
c
a
l
l
s
e
x
c
l
u
d
e
n
<
1
i
n
c
l
u
d
e
l
a
b
e
l
s
f
(
n
)
=
3
f
(
n
-
1
f
(
n
-
1
)
)