I am getting WA in test#10. Can anyone help me??? Thanks in advance. :)

can you help me?
fail is on fifth test...
mikael@ubuntu:~/Desktop$ ./xx
1
1
mikael@ubuntu:~/Desktop$ ./xx
0
10
mikael@ubuntu:~/Desktop$ ./xx
2
2
mikael@ubuntu:~/Desktop$ ./xx
3
3
mikael@ubuntu:~/Desktop$ ./xx
4
22
mikael@ubuntu:~/Desktop$ ./xx
5
5
mikael@ubuntu:~/Desktop$ ./xx
6
23
mikael@ubuntu:~/Desktop$ ./xx
8
24
mikael@ubuntu:~/Desktop$ ./xx
9
33
mikael@ubuntu:~/Desktop$ ./xx
10
25
mikael@ubuntu:~/Desktop$ ./xx
20
45
mikael@ubuntu:~/Desktop$ ./xx
25
55
mikael@ubuntu:~/Desktop$ ./xx
30
56
mikael@ubuntu:~/Desktop$ ./xx
45
59
mikael@ubuntu:~/Desktop$ ./xx
60
256
mikael@ubuntu:~/Desktop$ ./xx
105
357
mikael@ubuntu:~/Desktop$ ./xx
108
269
mikael@ubuntu:~/Desktop$

Mikael, according your outputs: 2->2, 3->3, and why is 4->22? Maybe 4->4 is right answer?

Input: 22
Output: -1