distribute	reads
0-500	2269511
500-800	1388482
800-1000	415166
1000-1200	224211
1200-1400	119857
1400-1600	64604
1600-1800	34075
1800-2000	18666
2000-2200	10127
2200-2400	5623
2400-2600	3168
2600-2800	1847
2800-3000	1136
>3000	1869
