var s:string;
    s1:array [1..100] of char;
    a,b:array [1..100] of integer;
    i,j,n:integer;
begin
  readln(s);
  n:=length(s);
  for i:=1 to n do
    a[i]:=ord(s[i])-97;
  for i:=n downto 2 do         {24+x-26 = 17}
    begin
      b[i]:=(a[i]+26-a[i-1])mod 26;
      s1[i]:=chr(b[i]+97);
    end;
  s1[1]:=chr(((a[1]-5)mod 26)+97);
  for i:=1 to n do
    write(s1[i]);
  readln;
end.
WA on 4th test!!!

lol got AC now....