Largest Prime Finder

You are given an integer n. Your task is to find the largest prime number that is less than or equal to n. If n is not a positive integer greater than 1, then output Not valid.

Recall that a prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. In mathematical notation, a number p is prime if:

\(p > 1\) and for every \(d \in \mathbb{N}\) with \(1 < d < p\), we have \(d \nmid p\).

For example:

• For n = 10, the largest prime \(\leq 10\) is 7.
• For n = 29, since 29 itself is prime, the answer is 29.
• For edge cases like n = 1 or negative numbers, the output should be Not valid.

Write a program that reads the input from stdin and prints the result to stdout.

inputFormat

Input consists of a single integer n provided via standard input.

outputFormat

Output the largest prime number less than or equal to n if it exists; otherwise, output the string Not valid.## sample

10

7