Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Great but doesn't last a month

I love this whole litterbox system, but I find I have to change it every 2 1/2 weeks instead of every month. I only have one cat and he is a tad overweight, so that may account for the frequent changes. I wihs you could buy these refills is the grocery store or at Wal-Mart or Target, but they work well. Absolutely no odor until it's time to change!