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