import os, sys
if os.path.exists("input.txt"):
  sys.stdin = open('input.txt', 'r')
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

def inp(): return readline().rstrip().decode('utf-8')
def inps(): return map(int, inp().split())

inp()
B = list(inps())
if 0 in B:
  print(1)
  print(B.index(0) + 1)
  exit()

di = {}
di.setdefault(0, 0)
xr = 0
for i, v in enumerate(B):
  xr ^= v
  if xr in di:
    print(i - di[xr] + 1)
    for j in range(di[xr], i + 1):
      print(j + 1, end = ' ')
    print()
    exit()
  di[xr] = i

print(-1)