CF660E.Different Subsets For All Tuples

For a sequence $a$ of $n$ integers between $1$ and $m$ , inclusive, denote $f(a)$ as the number of distinct subsequences of $a$ (including the empty subsequence).

You are given two positive integers $n$ and $m$ . Let $S$ be the set of all sequences of length $n$ consisting of numbers from $1$ to $m$ . Compute the sum $f(a)$ over all $a$ in $S$ modulo $10^{9}+7$ .

The only line contains two integers $n$ and $m$ ( $1<=n,m<=10^{6}$ ) — the number of elements in arrays and the upper bound for elements.

Print the only integer $c$ — the desired sum modulo $10^{9}+7$ .