real work(27),y(4)
       integer iwork(5)
       common /aaa/gammam
       external f
       Open(10,file="kepler.in")
       open(20,file="kepler.out")
       Read(10,*) relerr,abserr,amass,gamma,nt,dt,y
       gammam=amass*gamma
       neqn=4
       t=0
       t=tout
       iflag=1
       CALL rkf45(f,neqn,y,t,tout,relerr,abserr,iflag,work,iwork)
       iflag=2
       do i=1,nt
       iflag=2
       tout=t+dt
       CALL rkf45(f,neqn,y,t,tout,relerr,abserr,iflag,work,iwork)
       t=tout
       print "(5e15.5)",t,y
       enddo
       stop
       end

       subroutine f(t,y,dy)
       common /aaa/gammam
       real y(4),dy(4)
       dy(1)=y(3)
       dy(2)=y(4)
       dy(3)=-gammam*y(1)/sqrt(y(1)**2+y(2)**2)**3
       dy(4)=-gammam*y(2)/sqrt(y(1)**2+y(2)**2)**3
       return
       end