import math as m
ans = []
def flip(i):
    b = (i + m.ceil(len(a)/2)-1 % len(a)) + 1
    c = (i - m.ceil(len(a)/2) - 1 % len(a)) + 1
    ans.append(i)
    if(a[i]==0):
        a[i] = 1
    else:
        a[i] = 0
    if((b>0) and b<len(a)):
        if(a[b] == 0):
            a[b] = 1
        else:
            a[b] = 0
    if((c>0) and c<len(a)):
        if(a[c] == 0):
            a[c] = 1
        else:
            a[c] = 0
n = input("")
a = input("").split(" ")

a = [int(i) for i in a]
l = int(n)-1
if(a[(l)] == 1):
    flip((len(a)-1))
r = int((len(a)-1)/2)        
for i in range(int(n)*7):
    while(r>1):
        if(a[r]==0):
            flip(r)
            break
        else:
            r = int(r/2)
            
if(len(ans) != 0):
    print(len(ans))
    print(ans)
else:
    print(-1)