Memory system

A memory system comprising:

• a semiconductor memory device;
• and
• a controller configured to control the semiconductor memory device,
• wherein the semiconductor memory device includes:
• a plurality of memory cells capable of storing at least first to third data;
• and
• a word line coupled to the plurality of memory cells,
• wherein
• the first data is determined by a first read operation including a first read level,
• the second data is determined by a second read operation including a second read level,
• the third data is determined by a third read operation including a third read level, and
• the controller is configured to control the semiconductor memory device to perform a forth read operation including the first and second read levels in a search operation for first to third read voltages corresponding to the first to third read levels, respectively.