Please use code tags for posting your code. Also give a brief description of your algorithm, approach. Its easier for people to read and debug your code this way.
you shold use #include instead of #include<iostream.h>
no need to add if(n>0 && n<=2000) and if(st>=0 && st<=2000)
and finally in if(n%5==0 && n<st) it should be (n+0.50<2000)