def main():
  from sys import stdin
  import math
  readline=stdin.readline
  n = int(readline())
  A = list(map(int, readline().split()))
  mod = 10**9 + 7
  ans = 1
  for i in range(n):
    a = A[i]
    if a == 0:
      print(-1)
      exit()
    elif a >= 4:
      print(mod)
      exit()
    elif a == 1:
      continue
    elif a == 2:
      ans *= 4
    elif a == 3:
      ans *= 729
    if ans > mod:
      ans = mod % ans
  print(mod % ans)
main()