Here's the answer:
“寒くない”
(samukunai)
Watch a real native speaker say it:
Here's how it sounds in a textbook:
Fun fact: the hundreds of thousands of people learning Japanese with Memrise get this phrase correct 93.52% of the time!
(samukunai)
Fun fact: the hundreds of thousands of people learning Japanese with Memrise get this phrase correct 93.52% of the time!