import collections
import heapq
class Solution(object):
    def findNumberAppearingOnce(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        nums=collections.Counter(nums)
        x=heapq.nsmallest(1,nums,key=lambda x:nums[x])
        # print(x)
        return x[0]