: u>f 0 d>f ;
: f>u f>d drop ;
: nnf/ ( n1 n2 -- f ) swap u>f u>f f/ ;
: n-digits1 { n -- r }
  9e n 1- n nnf/ falog floor f- ;

: solve ( -- r )
  1 1e begin ( n rsum )
    dup n-digits1 fdup f0> while ( n rsum r )
      f+ 1+ repeat
  fdrop drop ;

Or you can use locals to reduce the stack load:

: solve ( -- r )
  1 1e begin { n f: rsum }
    n n-digits1 { f: r }
    r f0> while
      n 1+  r rsum f+ repeat
  rsum ;

But given the tone of your posting, I guess you think that the stack
makes that difficult to follow, too.  Then you have two options:

1) Get some more practice in reading Forth or other stack-based
languages.  You may eventually get the hang of it.

2) Conclude that stack-based languages are not for you and stick with
whatever other language you like.