// индексы текущих элементов.
	private int i1,i2,i3;

	public Integer GetNext() {

		Integer next1 = (i1 < list1.size()) ? list1.get(i1) : Integer.MAX_VALUE;
		Integer next2 = (i2 < list2.size()) ? list2.get(i2) : Integer.MAX_VALUE;
		Integer next3 = (i3 < list3.size()) ? list3.get(i3) : Integer.MAX_VALUE;
		
		
		// min(next1, next2, next3)
		Integer next = Math.min(next1, Math.min(next2, next3));
		
		if(next.equals(Integer.MAX_VALUE)) {
			throw new NoSuchElementException();
		} else if(next.equals(next1)) {
			i1++;
		} else if(next.equals(next2)) {
			i2++;
		} else if(next.equals(next3)) {
			i3++;
		}
		
		return next;
	}

	// текущие значения итераторов
	private Integer v1, v2, v3;

	public Integer next() {
		v1 = (v1 == null && iterator1.hasNext()) ? iterator1.next() : v1;
		v2 = (v2 == null && iterator2.hasNext()) ? iterator2.next() : v2;
		v3 = (v3 == null && iterator3.hasNext()) ? iterator3.next() : v3;
		
		// min(next1, next2, next3)
		Integer v12 = min(v1, v2);
		Integer next = min(v12, v3);
		
		if (next == null) {
			throw new NoSuchElementException();
		} else if (next.equals(v1)) {
			v1 = null;
		} else if (next.equals(v2)) {
			v2 = null;
		} else if (next.equals(v3)) {
			v3 = null;
		}

		return next;
	}