If you ever wonder what a perl error or warning message means, just add "use diagnostics;" (or manually look in perldoc perldiag). For this one, it shows:

    (W once) Typographical errors often show up as unique variable nam
+es.
    If you had a good reason for having a unique name, then just menti
+on it
    again somehow to suppress the message.  The our declaration is
    provided for this purpose.

    NOTE: This warning detects symbols that have been used only once s
+o $c, @c,
    %c, *c, &c, sub c{}, c(), and c (the filehandle or format) are con
+sidered
    the same; if a program uses $c only once but also uses any of the 
+others it
    will not trigger this warning.
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The (W once) means its a warning, and no warnings 'once'; will turn it off (and any other warnings in the once category) for a given scope.

Unfortunately our won't work with filehandles; if it really isn't mistyped, you can also say use vars "*INPUT";