interval based count

Hi,

I have a file with 4 million rows. what i am trying to achieve is for every 1000 interval count the number of rows and display it

i/p

12
200
400
750
1000
1500
1800
2200
2345
2600
2896
3020
3400
3689
3977

o/p

1-1000  5
1001-2000   2
2001-3000   4
3001-4000   4

Thanks,