10
0 a 1
0 b 2
1 a 2
1 b 3
2 a 3
2 b 4
3 a 4
3 b 5
4 a 5
4 b 6
5 a 6
5 b 7
6 a 7
6 b 8
7 a 8
7 b 9
8 a 9
8 b 0
9 a 0
9 b 1
0 5
3
2
4
6