Description

Input

The input consists of a single line, which contains two integers $n$, $x$ ($2 \leq n \leq 4000$, $1 \leq x < 1\,000\,000\,007$).

Output

Let $a_{m,k}$ be the answer for the pair $(m, k)$, modulo $998\,244\,353$.

Let $$\large S = \sum_{m=3}^{n+1} \sum_{k=0}^{n-1} a_{m,k}x^{mn+k}\phantom{0}.$$

Output a single line with an integer: $S$ modulo $1\,000\,000\,007$.

Note that using two different modulos is intentional. We want you to calculate all the $a_{m,k}$ modulo $998\,244\,353$, then treat them like integers in the range $[0, 998\,244\,352]$, and hash them modulo $1\,000\,000\,007$.

3 2

4 1000000000

8 327869541

4000 1149333

77824

30984329

85039220

584870166

Note

In the first test case, the answers for all $(m, k)$ are shown in the following table:

• The answer for $(m, k) = (3, 2)$ is $6$, because for every permutation of length $3$, $a_i + a_{i+1} \geq 3$ exactly $2$ times.
• The answer for $(m, k) = (4, 2)$ is $2$. In fact, there are $2$ permutations of length $3$ such that $a_i + a_{i+1} \geq 4$ exactly $2$ times: $[1, 3, 2]$, $[2, 3, 1]$.

Therefore, the value to print is $2^9 \cdot 0 + 2^{10} \cdot 0 + 2^{11} \cdot 6 + 2^{12} \cdot 0 + 2^{13} \cdot 4 + 2^{14} \cdot 2 \equiv 77\,824 \phantom{0} (\text{mod} \phantom{0} 1\,000\,000\,007)$.

In the second test case, the answers for all $(m, k)$ are shown in the following table:

• The answer for $(m, k) = (5, 1)$ is $4$. In fact, there are $4$ permutations of length $4$ such that $a_i + a_{i+1} \geq 5$ exactly $1$ time: $[2, 1, 3, 4]$, $[3, 1, 2, 4]$, $[4, 2, 1, 3]$, $[4, 3, 1, 2]$.

In the third test case, the answers for all $(m, k)$ are shown in the following table: