The little ant lived in the nest for a long time and wanted to go out and break into the world. So it bid farewell to its friends and took some food to the big city it longed for.

One day it came to the digital city. As soon as the little ant stepped into the gate, he was stopped by two guys with round heads and brains. At first glance, it is two "0s". Two zeros say at the same time: "Who wants to enter the digital city? Take out the IQ certificate first. If not, we will pass this level first. " The little ant is curious: What are you doing here? Should I have a test before I enter the door? Ok, let me try. Zero guards became an empty "nine squares". It called many numbers and said to the little ant, "Fill in 1-9 in the grid, so that the sum of each row and column will be equal." When the little ant saw it, he laughed: "Can this kind of thing baffle me?" Say that finish, a stroke of a pen, write out: 4.

nine

2

three

five

seven

eight

1

six

The guard disappeared at once, and a wide avenue appeared in front of the little ant.