13. (12 points) There are 16 students, who form a $4 \times 4$ square array. In a certain exam, their scores are all different. After the scores are announced, each student compares their score with their adjacent classmates (adjacent means front, back, left, and right, for example, a student sitting at a corner has only 2 classmates adjacent to him). If at most only 1 classmate's score is higher than his, he will consider himself “happy”. Then, the maximum number of students who will consider themselves “happy” is $\qquad$.
【Solution】Solution: In each $2 \times 2$ square, at most 3 people can be "happy", so out of 16 people, at most $16 \times \frac{3}{4}$ $=12$ people can be "happy",

Construct the following diagram. Among them, numbers 16 to 5, a total of 12 people, are "happy". Therefore, the answer is 12.