题目描述
Problem Statement
There is a monster with initial stamina N.
Takahashi repeatedly attacks the monster while the monster's stamina remains 1 or greater.
An attack by Takahashi reduces the monster's stamina by 2 with probability $\frac{P}{100}$
and by 1 with probability $1-\frac{P}{100}$.
Find the expected value, modulo 998244353 (see Notes), of the number of attacks before the monster's stamina becomes 0 or less.
Input
The input is given from Standard Input in the following format:
N P
Output
Find the expected value, modulo 998244353, of the number of Takahashi's attacks.
Constraints
- $1 \leq N \leq 2\times 10^5$
- $0 \leq P \leq 100$
- All values in the input are integers.
Sample Input 1
3 10
Sample Output 1
229596204
An attack by Takahashi reduces the monster's stamina
by 2 with probability $\frac{10}{100}=\frac{1}{10}$
and by 1 with probability $\frac{100-10}{100}=\frac{9}{10}$.
- The monster's initial stamina is 3.
- After the first attack, the monster's stamina is 2 with probability $\frac{9}{10}$ and 1 with probability $\frac{1}{10}$.
- After the second attack, the monster's stamina is 1 with probability $\frac{81}{100}, 0$ with probability $\frac{18}{100}$, and -1 with probability $\frac{1}{100}. With probability \frac{18}{100}+\frac{1}{100}=\frac{19}{100}$, the stamina becomes 0 or less, and Takahashi stops attacking after two attacks.
- If the stamina remains 1 after two attacks, the monster's stamina always becomes 0 or less by the third attack, so he stops attacking after three attacks.
Therefore, the expected value is $2\times \frac{19}{100}+3\times\left(1-\frac{19}{100}\right)=\frac{281}{100}. Since 229596204 \times 100 \equiv 281\pmod{998244353}$, print 229596204.
Sample Input 2
5 100
Sample Output 2
3
Takahashi's attack always reduces the monster's stamina by 2.
After the second attack, the stamina remains $5-2\times 2=1$, so the third one is required.
Sample Input 3
280 59
Sample Output 3
567484387
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分