View.Set ("graphics:max,max")
var x : array 1 .. 7 of int := init (0, 0, 0, 0, 0, 0, 0)
var y : array 1 .. 7 of int := init (0, 0, 0, 0, 0, 0, 0)
var mx, my, mb : int
var clickCount : int := 0
proc up
    loop
        mousewhere (mx, my, mb)
        exit when mb = 0
    end loop
end up
loop
    mousewhere (mx, my, mb)
    loop
        mousewhere (mx, my, mb)
        if mb = 1 and clickCount = 0 then
            drawfilloval (mx, my, 5, 5, blue)
            clickCount += 1
            up
            exit
        elsif mb = 1 and clickCount >= 4 then
            drawfilloval (mx, my, 5, 5, blue)
            drawline (mx, my, x (1), y (1), red)
            drawfilloval (x (5), y (5), 10, 10, white)
            drawline (x (4), y (4), x (3), y (3), white)
            up
            exit
        elsif mb = 1 and clickCount >= 1 then
            drawfilloval (mx, my, 5, 5, blue)
            drawline (mx, my, x (1), y (1), red)
            clickCount += 1
            up
            exit
        end if
    end loop
    x (1) := mx
    y (1) := my
    for decreasing i : 4 .. 2
        x (i) := x (i - 1)
        y (i) := y (i - 1)
    end for
end loop