Inserting a character at a certain position

[gbnine]

Hello.
I have a list of football matches which are displayed like this:

Oxford City
1
3
Slough
Dover
1
1
St. Albans

Is there a way I can insert a dash after each top number, like this?

Oxford City
1-
3
Slough
Dover
1-
1
St. Albans

Thank you.

[jfcherng]

regex find/replace (Ctrl+H): find ^(\d+)(?=\n\d+) and replace with \1-

[gbnine]

Thank you. I really appreciate it.