class Solution:
  def findNumber(self, nums):
    
    def swap(i, j):
      nums[i], nums[j] = nums[j], nums[i]

    for i in range(len(nums)):
      while nums[i] != i + 1 and nums[i] != nums[nums[i] - 1]:
        swap(i, nums[i] - 1)

    return nums[-1]