BEGIN
    INTEGER LIMIT = 100, door, stride;
    BOOLEAN ARRAY DOORS(1:LIMIT);
    TEXT intro;

    FOR stride := 1 STEP 1 UNTIL LIMIT DO
        FOR door := stride STEP stride UNTIL LIMIT DO
            DOORS(door) := NOT DOORS(door);

    intro :- "All doors closed but ";
    FOR door := 1 STEP 1 UNTIL LIMIT DO
        IF DOORS(door) THEN BEGIN
            OUTTEXT(intro); OUTINT(door, 0); intro :- ", "
        END;
    OUTIMAGE
END.