program dragged_fly_plot
      real m,k
      write(*,*)'Vx ?'
      read(*,*)vx
      write(*,*)'Vy ?'
      read(*,*) vy
      write(*,*)'Mass ?'
      read(*,*)m
      write(*,*)'Air friction ?'
      read(*,*)k
      if(pgopen('/xwin')<=0)stop
      call pgenv(0.0,10.0,0.0,10.0,1,0)
      dt=0.0001
      x=0.0
      y=5.0
      do while(y > 0.0)
        v=sqrt(vx*vx + vy*vy)
        f_d=(-1)*k*v
        ax_d=f_d*(vx/v)/m
        ay_d=f_d*(vy/v)/m
        ax=0.0 + ax_d
        ay=-9.8 + ay_d
        vx=vx+ax*dt
        vy=vy+ay*dt
        x=x+vx*dt
        y=y+vy*dt
        call pgpt(1,x,y,20)
      end do
      write(*,*)'Final hight :',y
      write(*,*)'Final distance :',x
      call pgclos
      end