题目描述
Problem Statement
For a sequence of length $N, A = (A_1,A_2,\dots,A_N),$ consisting of integers between 1 and N, inclusive, and an integer i\ $(1\leq i \leq N)$, let us define a sequence of length $10^{100}, B_i=(B_{i,1},B_{i,2},\dots,B_{i,10^{100}})$, as follows.
- B_{i,1}=i.
- B_{i,j+1}=A_{B_{i,j}}\ $(1\leq j<10^{100})$.
Additionally, let us define S_i as the number of distinct integers that occur exactly once in the sequence B_i.
More formally, S_i is the number of values k such that exactly one index j\ $(1\leq j\leq 10^{100}) satisfies B_{i,j}=k$.
You are given an integer N. There are N^N sequences that can be A. Find the sum of $\displaystyle \sum_{i=1}^{N} S_i$ over all of them, modulo M.
Input
The input is given from Standard Input in the following format:
N M
Output
Print the answer as an integer.
Constraints
- $1\leq N \leq 2\times 10^5$
- $10^8\leq M \leq 10^9$
- N and M are integers.
Sample Input 1
4 100000000
Sample Output 1
624
As an example, let us consider the case A=(2,3,3,4).
- For i=1: we have $B_1=(1,2,3,3,3,\dots)$, where two integers, 1 and 2, occur exactly once, so S_1=2.
- For i=2: we have $B_2=(2,3,3,3,\dots)$, where one integer, 2, occurs exactly once, so S_2=1.
- For i=3: we have $B_3=(3,3,3,\dots)$, where no integers occur exactly once, so S_3=0.
- For i=4: we have $B_4=(4,4,4,\dots)$, where no integers occur exactly once, so S_4=0.
Thus, we have $\displaystyle \sum_{i=1}^{N} S_i=2+1+0+0=3$.
If we similarly compute $\displaystyle \sum_{i=1}^{N} S_i$ for the other 255 sequences, the sum of this value over all 256 sequences is 624.
Sample Input 2
7 1000000000
Sample Output 2
5817084
Sample Input 3
2023 998244353
Sample Output 3
737481389
Print the sum modulo M.
Sample Input 4
100000 353442899
Sample Output 4
271798911
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分