Overthinking

overthinking.txt

This problem can be solved by pre-school children in
five to ten minutes, by programmers in a hour and by
people with higher education... well, check it yourself!

8809 = 6            5555 = 0
7111 = 0            8193 = 3
2172 = 0            8096 = 5
6666 = 4            1012 = 1
1111 = 0            7777 = 0
3213 = 0            9999 = 4
7662 = 2            7756 = 1
9313 = 1            6855 = 3
0000 = 4            9881 = 5
2222 = 0            5531 = 0
3333 = 0            2581 = ???