distribute	reads
0-500	1568362
500-800	670869
800-1000	153992
1000-1200	80764
1200-1400	47602
1400-1600	30464
1600-1800	20783
1800-2000	14915
2000-2200	11156
2200-2400	8644
2400-2600	6860
2600-2800	5545
2800-3000	4454
>3000	26307
