for _ in range(int(input())):
n = int(input())
l = [*map(int, input().split())]
d = l.count(2)
if d % 2 == 1:
print(-1)
continue
d //= 2
c = 0
for idx, i in enumerate(l):
if i == 2:
c += 1
if c == d:
print(idx + 1)
break