I do not understand why the following example, as a result shows six in C Challenge?

Question

Could someone explain it to me? Thank you in advance.
https://code.sololearn.com/cIxqDI24hN24/?ref=app

Answer 1

ravilnicki ,Thanks 👍

Answer 2

Egor Tonchev(EGO)

Because 1 + 2 + 3 = 6