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