N = int(input())
A = list(map(int, input().split()))
MOD = 10 ** 9 + 7
ans = 0
cur = 1
for i in range(N - 1):
    cur = (cur * A[i]) % MOD
    ans += (cur * 2 * pow(3, N - i - 2, MOD)) % MOD
cur = (cur * A[-1]) % MOD
print((ans + cur) % MOD)