%!PS

% begin included library code
% see https://codeberg.org/Firedrake/postscript-libraries/
/a2s {
    2 dict begin
    /i exch def
    i length dup string /o exch def
    1 sub 0 exch 1 exch {
        dup i 3 -1 roll get o 3 1 roll put
    } for
    o
    end
} bind def

/test.end {
    ( ) print
    test.count 0 gt {
        (Passed ) print
        test.pass (...) cvs print
        (/) print
        test.count (...) cvs print
        ( \() print
        test.pass 100 mul test.count idiv (...) cvs print
        (%\)) print
        (\r\n) print
    } if
} bind def

/reverse {
    1 dict begin
    dup length /l exch def
    [ exch
      aload pop
      2 1 l {
          -1 roll
      } for
    ]
    end
} bind def

/deepeq {
    2 dict begin
    /a exch def
    /b exch def
    a type b type eq {
        a type /dicttype eq {
            a length b length eq {
                <<
                    a {
                        pop
                        true
                    } forall
                    b {
                        pop
                        true
                    } forall
                >>
                true exch
                {
                    pop
                    dup a exch known {
                        dup b exch known {
                            dup a exch get exch b exch get deepeq not {
                                pop false
                            } if
                        } {
                            false
                        } ifelse
                    } {
                        false
                    } ifelse
                } forall
            } {
                false
            } ifelse
        } {
            a type dup /arraytype eq exch /stringtype eq or {
                a length b length eq {
                    true
                    0 1 a length 1 sub {
                        dup a exch get exch b exch get deepeq not {
                            pop false
                            exit
                        } if
                    } for
                } {
                    false
                } ifelse
            } {
                a b eq
            } ifelse
        } ifelse
    } {
        false
    } ifelse
    end
} bind def

/test {
    /test.count test.count 1 add def
    {
        /test.pass test.pass 1 add def
    } {
        ( ) print
        test.count (....) cvs print
        (-fail) print
    } ifelse
} bind def

/s2a {
    [ exch { } forall ]
} bind def

/test.start {
    print (:) print
    /test.pass 0 def
    /test.count 0 def
} bind def

/alloccvs {
    2 dict begin
    /n exch def
    /a 1 def
    n
    dup 0 lt {
        /a a 1 add def
        neg
    } if
    {
        dup 10 lt {
            exit
        } if
        /a a 1 add def
        10 idiv
    } loop
    pop
    n a string cvs
    end
} bind def


% end included library code

/closestpalindrome {
    0 dict begin
    cvi /n exch def
    /delta -1 def
    {
        /q n delta add alloccvs def
        q dup s2a reverse a2s deepeq {
            q
            exit
        } if
        /delta delta neg def
        delta 0 lt {
            /delta delta 1 sub def
        } if
    } loop
    end
} bind def

(closestpalindrome) test.start
(123) closestpalindrome (121) eq test
(2) closestpalindrome (1) eq test
(1400) closestpalindrome (1441) eq test
(1000) closestpalindrome (999) eq test
test.end