AtCoder Grand Contest 067
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Problem Statement
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You are given an integer $N$ and prime $P$.
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We call a sequence of $N$ intervals $([L_1,R_1] ,[L_2,R_2], \cdots, [L_N,R_N])$ good if and only if both of the followings are satisfied:
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$1\le L_i\le R_i\le N$holds for all$1\le i\le N$.- There exists a unique permutation
$x=(x_1,x_2,\cdots,x_N)$of$(1,2,\cdots,N)$such that$L_i\le x_i\le R_i$holds for all$1\le i\le N$.
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Count the number, modulo $P$, of good sequences of intervals.
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Constraints
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$2 \leq N \leq 5000$$10^9<P<1.01\times 10^9$$P$is prime.- All input values are integers.
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Input
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Input is given from Standard Input in the following format:
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N P
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Output
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Print the answer.
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样例
Input #1
2 1005488041
Output #1
6
The following $6$ sequences are good:
- $([1,1],[2,2])$
- $([1,2],[2,2])$
- $([1,1],[1,2])$
- $([2,2],[1,1])$
- $([2,2],[1,2])$
- $([1,2],[1,1])$
Input #2
5 1005488041
Output #2
102960
Input #3
100 1005488041
Output #3
47599495
Input #4
1000 1005488041
Output #4
632708165
题目信息
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