Why timelimit on 3rd test?
My program listing:

program hack;
var
ar : array[1..100] of byte;
i,n : integer;
word : string;
begin
readln(word);
n := length(word);
for i:=1 to n do
    begin
         ar[i] := ord(word[i]) - 97;
    end;

begin
      for i:=2 to n do
      begin
           if ar[i] < ar[i-1] then
           while ar[i] < ar[i-1] do ar[i]:= ar[i] + 26;
      end;
end;
for i:= 0 to n-2 do
    begin
         ar[n-i] := ar[n-i] - ar[n-i-1];
    end;
ar[1] := ar[1] - 5;

for i := 1 to n do
    begin
         word[i] := chr(97+ar[i]);
    end;

writeln(word);
end.