program fly_path
      idummy=pgopen('/xwin')
      call pgenv(0.0,10.0,0.0,10.0,1,0)

      write(*,*)'vx?'
      read(*,*)vx
      write(*,*)'vy?'
      read(*,*)vy

      dt=0.0001

      y=1.0
      x=0.0
      
      ax=0
      ay=-9.8

      do while (y>0)
        vx=vx+ax*dt
        vy=vy+ay*dt
        x=x+vx*dt
        y=y+vy*dt
        call pgpt(1,x,y,-1)
      end do

      write(*,*) 'distance=',x,'  hight=',y
      call pgclos
      end