program main
      implicit none
      real(8) x,v,f,t,dt,t_fin,x_old,v_old
      integer Nt,it
      real(8) m,k
c
      t_fin=10d0
      Nt=100
      dt=t_fin/Nt
      m=1d0
      k=1d0
c
      t=0d0
      x_old=1d0
      v_old=0d0
c
      open(10,file='Newton_Euler.dat')
      write(10,'(3e16.6E3)')t,x_old,v_old
c
      do it=1,Nt
      t=dt*it
c
      x=x_old+v_old*dt
      v=v_old-k/m*x_old*dt
c
      x_old=x
      v_old=v
c
      write(10,*)t,x_old,v_old
c
      end do
c
      close(10)
c
      end program main