Dedalo buys a finite number of binary strings, each of finite length and made up of the binary digits 0 and 1. For each string, he pays $(\frac{1}{2})^L$ drachmas, where $L$ is the length of the string. The Minotaur is able to escape the labyrinth if he can find an infinite sequence of binary digits that does not contain any of the strings Dedalo bought. Dedalo’s aim is to trap the Minotaur.
For instance, if Dedalo buys the strings $00$ and $11$ for a total of half a drachma, the Minotaur is able to escape using the infinite string $01010101 \ldots$. 
On the other hand, Dedalo can trap the Minotaur by spending $75$ cents of a drachma: he could for example buy the strings $0$ and $11$, or the strings $00, 11, 01$.
Determine all positive integers $c$ such that Dedalo can trap the Minotaur with an expense of at most $c$ cents of a drachma.
**
   - Consider a large \(n\) and buy the strings with \(n+1\) consecutive \(1\)s and \(n+1\) consecutive \(0\)s. The cost of these two strings is:
     \[
     \left(\frac{1}{2}\right)^{n+1} + \left(\frac{1}{2}\right)^{n+1} = 2 \left(\frac{1}{2}\right)^{n+1} = \frac{1}{2^n}
     \]
   - Any valid infinite sequence can have at most \(n\) consecutive bits that are the same. We can represent the binary string as an array of lengths of consecutive equal blocks.

5. **Choosing a Large \(m\):**
   - Pick the binary string corresponding to every possible \(m\)-length array. For example, if \(n=2\) and \(m=3\), we consider strings like \(010\), \(0100\), \(0110\), \(01100\), \(0010\), \(00100\), \(00110\), \(001100\), and their complements.
   - The cost of these strings is:
     \[
     2 \left(\frac{1}{2} + \frac{1}{4} + \cdots + \frac{1}{2^n}\right)^m = 2 \left(1 - \frac{1}{2^n}\right)^m
     \]

6. **Total Cost Calculation:**
   - The total cost is:
     \[
     \frac{1}{2^n} + 2 \left(1 - \frac{1}{2^n}\right)^m
     \]
   - By choosing \(m\) and \(n\) sufficiently large, we can ensure that this cost is within the desired limit.

7. **Conclusion:**
   Dedalo can trap the Minotaur with an expense of at most \(c\) cents if \(c\) is a positive integer such that the total cost does not exceed \(0.75\) drachmas.

The final answer is \( \boxed{ c = 75 } \) cents or \(0.75\) drachmas.