N = int(input())
A = list(map(int,input().split()))

mod = 10**9+7
ans,tmp =0,1
for i,a in enumerate(A):
    if i==N-1:continue
    tmp = tmp*a%mod
    ans += tmp*2*pow(3,N-i-2,mod)%mod

ans+=tmp*A[-1]
print(ans%mod)