program Project2;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
   s,a:string;
   x,y,l,kk,k,k1,i,n:integer;
   f1,f2:text;
begin
  assign(f1,'substr.dat');
  reset(f1);
  readln(f1,a);
  assign(f2,'substr.sol');
  rewrite(f2);
  n:=length(a);
  x:=1; y:=1;
  k1:=1; kk:=1;
  l:=1;
  for i:=2 to n do
  begin
  k:=k1;
  while a[i]<>a[k] do
  k:=k+1;
  if k=i then begin kk:=kk+1; end else begin k1:=k+1; kk:=i  end;
  if kk-k1+1>l then begin x:=k1;
  y:=kk; l:=kk-k1+1; end;
  end;
  for i:=x to y do
  write(f2,a[i]);
  close(f1);
  close(f2);
end.