Disclosed herein are related to a memory system and a method of operating the memory system. In one aspect, resistances of a first memory cell, a second memory cell, a third memory cell, and a fourth memory cell are individually set. In one aspect, the first memory cell and the second memory cell are coupled to each other in series between a first line and a second line, and the third memory cell and the fourth memory cell are coupled to each other in series between the second line and a third line. In one aspect, current through the second line according to a parallel resistance of i) a first series resistance of the first memory cell and the second memory cell, and ii) a second series resistance of the third memory cell and the fourth memory cell is sensed. According to the sensed current, multi-level data can be read.