real y(2) , work(15),mass,k
	integer iwork(5)
	common  beeta, omega0
	external f
	data pi/3.1415926536/
	open (10,file='sumb.in')
	open (20, file='sumb.out')
	neqn=2
	read(10,*)relerr,abserr,beeta,mass,k,dt,nt,y
	omega0=k/mass
	talg=0
	tlopp=0
	iflag=1
	call rkf45(f,neqn,y,talg,tlopp,relerr,abserr,iflag,work,iwork)

	do i =1,nt
	tlopp=talg+dt
	iflag=2
	call rkf45(f,neqn,y,talg,tlopp,relerr,abserr,iflag,work,iwork)
	talg=tlopp
	write(20,100) tlopp,y,mass*y(2)**2/2.,1.-k*cos(2.*pi*y(1))
     *  ,mass*y(2)**2/2.+1.-k*cos(2.*pi*y(1))
100	format(6f15.5)
	enddo
	stop
	end
	subroutine f(t,y,dy)
	real y(2),dy(2)
	common  beeta, omega0
	data pi/3.1415926536/
	dy(1)=y(2)
	dy(2)=-beeta*y(2)-2.*pi*omega0*sin(2.*pi*y(1))
	return
	end