1.B2.C3.A4.A5.B6.B7.B8.D9.D10.B11.A12.B13.C14.A15.A16.C17.B18.B19.B20.B
B C A A B B B D D A C B C D A C B B A B
B C A A B B B D D B C B C A C C B B B B
n
1b2c3a