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