20
0 a 3
0 b 0
1 a 8
1 b 7
2 a 7
2 b 4
3 a 3
3 b 17
4 a 2
4 b 18
5 a 13
5 b 1
6 a 0
6 b 2
7 a 6
7 b 7
8 a 16
8 b 19
9 a 0
9 b 17
10 a 6
10 b 17
11 a 13
11 b 7
12 a 14
12 b 18
13 a 8
13 b 0
14 a 5
14 b 13
15 a 10
15 b 8
16 a 4
16 b 6
17 a 10
17 b 3
18 a 2
18 b 12
19 a 3
19 b 11
11 19
20
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19