AtCoder Beginner Contest 281
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Problem Statement
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Takahashi has $A$ kinds of level-$1$ gems, and $10^{10^{100}}$ gems of each of those kinds.
For an integer $n$ greater than or equal to $2$, he can put $n$ gems that satisfy all of the following conditions into a cauldron to generate a level-$n$ gem in return.
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- No two gems are of the same kind.
- Every gem's level is less than
$n$. - For every integer
$x$greater than or equal to$2$, there is at most one level-$x$gem.
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Find the number of kinds of level-$N$ gems that Takahashi can obtain, modulo $998244353$.
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Here, two level-$2$ or higher gems are considered to be of the same kind if and only if they are generated from the same set of gems.
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- Two sets of gems are distinguished if and only if there is a gem in one of those sets such that the other set does not contain a gem of the same kind.
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Any level-$1$ gem and any level-$2$ or higher gem are of different kinds.
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Constraints
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$1 \leq N \leq 2 \times 10^5$$1 \leq A \leq 10^9$$N$and$A$are integers.
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Input
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The input is given from Standard Input in the following format:
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N A
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Output
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Print the answer.
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样例
Input #1
3 3
Output #1
10
Here are ten ways to obtain a level-$3$ gem.
- Put three kinds of level-$1$ gems into the cauldron.
- Takahashi has three kinds of level-$1$ gems, so there is one way to choose three kinds of level-$1$ gems. Thus, he can obtain one kind of level-$3$ gem in this way.
- Put one kind of level-$2$ gem and two kinds of level-$1$ gems into the cauldron.
- A level-$2$ gem can be obtained by putting two kinds of level-$1$ gems into the cauldron.
- Takahashi has three kinds of level-$1$ gems, so there are three ways to choose two kinds of level-$1$ gems. Thus, three kinds of level-$2$ gems are available here.
- There are three kinds of level-$2$ gems, and three ways to choose two kinds of level-$1$ gems, so he can obtain $3 \times 3 = 9$ kinds of level-$3$ gems in this way.
Input #2
1 100
Output #2
100
Input #3
200000 1000000000
Output #3
797585162
题目信息
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