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

ans += n*A[-1]
ans %= MOD

print(ans)