Prime number

A natural number X is considered a derivative of another natural number N if X is either identical to N or can be formed by removing some digits from the decimal representation of N. For instance, the derivatives of the number 1024 include 1, 2, 4, 10, 12, 14, 24, 102, 104, 124, and 1024. Given a natural number N, your task is to find the largest prime number P that is a derivative of N. If none of the derivatives of N are prime, then P should be set to 0. A natural number P is defined as prime if P≠1 and it has no divisors other than 1 and P itself.

Input

The input consists of a single line containing the number N (0 < N < 10^9).

Output

The output should be the number P.

Examples