5.4. Find the sum of the digits in the decimal representation of the integer part of the number $\sqrt{\underbrace{44.44}_{2018} \underbrace{88 \ldots 88}_{2017} 9}$.
Answer: 12109 (the number from the condition of the problem is equal to $\underbrace{66 \ldots 66}_{2017} 7$ ).