import sys
input = sys.stdin.readline

N = int(input())
A = list(map(int, input().split()))
ans = 0
now = 1
MOD = 10**9+7

for i in range(N-1):
    now *= A[i]
    now %= MOD
    ans += now*2*pow(3, N-i-2, MOD)%MOD
    ans %= MOD

now *= A[-1]
now %= MOD
ans += now
ans %= MOD
print(ans)