The postman

A postman had to deal letters in a pretty strange neighbourhood. While he was doing it, he realized that the houses were ordered in an unusual way. They were stored in alphabetical order but next to each letter there were a random number. The postman was very curious, so he noted every letter with its number.

      A-5             F-3           K- 24        P- 12     U- 17      Z-26

       B-8           G-18          L-1             Q-19     V- 22

  C-9           H-21          M- 7          R-4        W-24

       D-10          I- 14          N-2           S- 11       X- 20

         E-23           J- 15      O- 13        T- 16        Y- 25

 When he arrived to the final house, he saw a woman and he asked her:

  -Sorry, how many people life in this strange neighbourhood?

  She answered 

 -The key is to think.