program free_fly
      write(*,*)'Vx ?'
      read(*,*)vx
      write(*,*)'Vy ?'
      read(*,*) vy
      dt=0.0001
      x=0.0
      y=10.0
      do while(y > 0.0)
        ax=0.0
        ay=-9.8
        vx=vx+ax*dt
        vy=vy+ay*dt
        x=x+vx*dt
        y=y+vy*dt
      end do
      write(*,*)'Final hight :',y
      write(*,*)'Final distance :',x
      end