{ fp }

{* 
 * Problem  : 	SUBSTR
 * Contest  : 	UOI-2006 (Dnepropetrovsk)
 * Type     : 	Solution
 * Date     : 	April 1, 2006
 * Author   : 	Sergey Savchuk
 * Language :	Pascal
 * Compiler :	Free Pascal
 * Algorithm:	Fast solution with buffered reading
 *}


Var fi,fo: Text; ff: File of char;
    a,ni:array['a'..'z'] of Longint;
    Buf: array[1..10000] of char;
    na,nii,i,ii,max,maxna,maxko: longint;
    ch: char;

Begin
     Assign(fi,'SUBSTR.DAT'); Reset(fi); SetTextBuf(fi,Buf,10000); na:=1;

     While not EOF(fi) do Begin Inc(ii);
      Read(fi,ch); if ch<'a' Then continue Else inc(i);
       if na<=a[ch] Then Begin na:=a[ch]+1; nii:=ni[ch] End;
       if i-na+1>max Then Begin Max:=i-na+1; maxna:=nii; maxko:=ii End;
       a[ch]:=i; ni[ch]:=ii
     End; Close(fi);

     Assign(fo,'SUBSTR.SOL'); ReWrite(fo);
     Assign(ff,'SUBSTR.DAT'); Reset(ff); Seek(ff,maxna); ii:=maxna+1;
     For ii:=maxna+1 to maxko do Begin
      Read(ff,ch); if ch<'a' Then continue Else Write(fo,ch);
     End; Writeln(fo); Close(fo)
End.