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Let's call a number palindromic if it reads the same from right to left as it does from left to right. For example, the number 78887 is palindromic. Find all five-digit palindromic numbers that use only the digits 1 and 0.

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Note that the leading digit cannot be 0. Therefore, the first and last positions must definitely be the digit 1. It is not difficult to calculate that the problem has four solutions - two solutions with zero in the middle and two solutions with one in the middle (students are not required to prove this).

## Answer

$10001,10101,11011,11111$.
[ Semi-invariants
Problem