local n = io.read("*n")
local a = {}
for i = 1, n do
  a[i] = io.read("*n")
end
local ret = 1
for i = 1, n do
  if 4 <= a[i] then
    print(1000000007) os.exit()
  elseif 3 == a[i] then
    ret = ret * 729
  elseif 2 == a[i] then
    ret = ret * 4
  elseif 0 == a[i] then
    print(-1) os.exit()
  end
  if 1000000007 < ret then
    print(1000000007) os.exit()
  end
end
print(1000000007 % ret)