public void set(int pos, int val) {
			if (start == end && start == pos) {
				mulVal = val;
			} else {
				int mid = (start + end) / 2;
				if (pos <= mid)
					left.set(pos, val);
				else
					right.set(pos, val);
				mulVal = left.mulVal*right.mulVal;
			}
		}