a simple csh script

I am looking for an example of csh script to test the input is a positive integer. Any input can help!!! Thanks!

My one didn't work
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echo -n "Please enter a positive integer "
set input=$<
if ($input contains '-' || $input contains '.') then
    echo "wrong input"
else
   echo "input accepted"
endif
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my problem is that I don't know how to grep the $input whether or not has a symbol minus sign i.e. '-' or decimal sign i.e. '.'