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Codeforces (c) Copyright 2010-2026 Михаил Мирзаянов
Соревнования по программированию 2.0
Время на сервере: 19.05.2026 19:46:09 (g1).
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What about 90,90,90,90,90,90,90,90,90,90,442.
People talk about conspiracy theories where Hitler is still alive. But after this comment they'll be talking about theories where Einstein's still alive.
Since the maximum sum of digits of a k-digit decimal number representation is 9k, the minimum number of digits of the decimal representation of N and 2N should be 13 digits and 14 digits, respectively.
UPDATE: It turns out that it is sufficient to concatenate two instances of the number M = 1,994,999 whose sum of digits is 50, and whose double 2 M = 3,989,998 has sum of digits equal to 55. The concatenation leads to doubling the sum of digits as the most significant digit in M is less than 5, and no carry operation is performed between the two instances when M is doubled.
Therefore, the 14-digit decimal number N = 19,949,991,994,999 is a possible solution of the problem.
The following is the simple DP-based solution that generated such number.
https://ideone.com/LuMF89