Participants to an olympiad worked on $n$ problems. Each problem was worth a [color=#FF0000]positive [/color]integer number of points, determined by the jury. A contestant gets $0$ points for a wrong answer, and all points for a correct answer to a problem. It turned out after the olympiad that the jury could impose worths of the problems, so as to obtain any (strict) final ranking of the contestants. Find the greatest possible number of contestants.
1. **Understanding the Problem:**
   - We have \( n \) problems, each worth a positive integer number of points.
   - A contestant gets 0 points for a wrong answer and all points for a correct answer.
   - We need to determine the maximum number of contestants such that the jury can assign points to the problems to achieve any strict final ranking of the contestants.

2. **Key Insight:**
   - If two contestants answered the same set of problems correctly, they would have the same score regardless of the point values assigned to the problems. Therefore, each contestant must have a unique set of problems they answered correctly.

3. **Counting Unique Sets:**
   - There are \( 2^n \) possible subsets of \( n \) problems (including the empty set).
   - Each subset represents a unique combination of problems that a contestant could have answered correctly.

4. **Assigning Points:**
   - To ensure that each subset of problems corresponds to a unique score, we can assign points to the problems in powers of 2.
   - Specifically, assign problem 1 a value of \( 2^0 = 1 \) point, problem 2 a value of \( 2^1 = 2 \) points, problem 3 a value of \( 2^2 = 4 \) points, and so on, up to problem \( n \) with \( 2^{n-1} \) points.

5. **Ensuring Unique Scores:**
   - With this assignment, each subset of problems corresponds to a unique binary number, where each bit represents whether a problem was answered correctly (1) or incorrectly (0).
   - The binary number directly translates to a unique score, ensuring that no two contestants have the same score.

6. **Conclusion:**
   - Since there are \( 2^n \) unique subsets of problems, the maximum number of contestants that can be uniquely ranked is \( 2^n \).

The final answer is \( \boxed{2^n} \).