MOD = 10**9 + 7
N, M = gets.split.map(&:to_i)
A = gets.split.map(&:to_i)
A.unshift 0

fac = [1, 1]
fin = [1, 1]
inv = [0, 1]
(2 .. N + M + 10).each do |i|
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD
    fac[i] = fac[i - 1] * i % MOD
    fin[i] = fin[i - 1] * inv[i] % MOD
end

nCk = ->(n, k) {
    return 0 if n < k or n < 0 or k < 0
    fac[n] * (fin[k] * fin[n - k] % MOD) % MOD
}

ans = (1 .. N).sum { |k| nCk[M + N - k, N - k + 1] * A[k - 1] % MOD } % MOD
puts ans