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

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