It means you can't add the years you stayed less than 6 months in the country to your total days.
for example:
Year 1: 3 months stay
Year 2: 4 months stay
Year 3: full 1 year stay
Year 4: 8 months stay
Year 5: 3 months stay
Year 6: 2 months stay
Total: 1 year + 8 months only.