Thanks!
I dont know what i tried to achieve by finding the maximimum.

You need to find the number that occurs an odd amount of times, not the maximum amount of times.

You are failing this test:

array = [1, 1, 2, -2, 5, 2, 4, 4, -1, -2, 5]

Number of occurences = {1: 2, 2: 2, 4: 2, 5: 2, -1: 1, -2: 2}

-1 has an **odd** number of occurences, therefore you should return -1.