我们称一个字符串为“好字符串”，当且仅当该字符串不包含长度大于 $2$ 的回文子串。
现在我们想知道，在所有长度恰好为 $n$ 且字符集大小为 $m$ 的字符串中，有多少个不同的好字符串（不一定需要使用字符集中的所有字符）。
输入格式
仅一行，包含两个整数 $n, m$ ($1 \le n \le 10^6, 1 \le m \le 10^9$)。
输出格式
输出一个整数，表示不同的好字符串的数量，答案对 $1000000007$ 取模。
样例
输入样例 1
3 3
输出样例 1
18
QOJ.ac
QOJ
Limite de temps : 1.0 s
Limite de mémoire : 256 MB
Points totaux : 100
Hackable ✓
#15201. 好的字符串
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