40
0  0
0  2
0  4
0  6
0  8
0  10
0  12
0  14
0  16
0  18
0  20
0  22
0  24
0  26
0  28
0  30
0  32
0  34
0  36
0  38
12  38
12  36
12  34
12  32
12  30
12  28
12  26
12  24
12  22
12  20
12  18
12  16
12  14
12  12
12  10
12  8
12  6
12  4
12  2
12  0