N
N2
N
2
N
b
aS
2
N
3
3
2
2
a
2
2
2
N
2
3
S24
3
2
2
S4
2
2
2
N
S
b
3
4
N
3
a
3
S4
)
2
S2
24
2
2
4
4
O
3
2
.
N
3
S
a
2
2
S2
a
3
S2
N
3
S
N
3
2
a
N
2
1995:91
3
aS
3
1
2
S
1995:91
3
2
S
S 2
2
3 2
S
2
S2
a
3
S
3
N
N
S4,
3
2
2
1
a
a
3
3
S2
2
a
2
N2
S43 N
a
3
3