MathDB

The

1 \times 1

cells located around the perimeter of a

4 \times 4

square are filled with the numbers

1, 2, \ldots, 12

so that the sums along each of the four sides are equal. In the upper left corner cell is the number

1

, in the upper right - the number

5

, and in the lower right - the number

11

.
https://i.ibb.co/PM0ry1D/Kyiv-City-MO-2021-Round-1-10-2.png
Under these conditions, what number can be located in the last corner cell?
Proposed by Mariia Rozhkova

Problem Statement