题库练习 Primes or Palindromes?
← 上一题 下一题 →

A10060 | Primes or Palindromes?

时间限制1s
内存限制256MB
通过 / 提交0/0

题目描述

Rikhail Mubinchik believes that the current definition of prime numbers is obsolete as they are too complex and unpredictable. A palindromic number is another matter. It is aesthetically pleasing, and it has a number of remarkable properties. Help Rikhail to convince the scientific community in this!

Let us remind you that a number is called prime if it is integer larger than one, and is not divisible by any positive integer other than itself and one.

Rikhail calls a number a palindromic if it is integer, positive, and its decimal representation without leading zeros is a palindrome, i.e. reads the same from left to right and right to left.

One problem with prime numbers is that there are too many of them. Let's introduce the following notation: $π(n)$ — the number of primes no larger than $n$ , $rub(n)$ — the number of palindromic numbers no larger than $n$ . Rikhail wants to prove that there are a lot more primes than palindromic ones.

He asked you to solve the following problem: for a given value of the coefficient $A$ find the maximum $n$ , such that $π(n)<=A·rub(n)$ .

输入格式

The input consists of two positive integers $p$ , $q$ , the numerator and denominator of the fraction that is the value of $A$ (![](/uploads/luogu/CF568A/9295c3108204f6e95f501a0ea61a8fd226fe3001_0661b81d9faf.png), ![](/uploads/acgo/image/07b9417360407ca5_680a1d61ab74.jpeg)).

输出格式

If such maximum number exists, then print it. Otherwise, print "Palindromic tree is better than splay tree" (without the quotes).

输入输出样例

输入 #1
1 1
输出 #1
40
输入 #2
1 42
输出 #2
1
输入 #3
6 4
输出 #3
172
C++ 编辑器
输入
输出