program s;
 var str:string; fl:boolean; k,l,i,j:integer;
 alf:array['a'..'z'] of char;
 nat:array['0'..'9'] of char;
 lengths:array[1..10] of integer;

 begin
 read(str);k:=1;l:=1;
 for i:=1 to length(str) do
 begin
 fl:=false;
 for j:=1 to 25 do
 if str[i]=alf[j] then
 fl:=true;
 for j:=1 to 10 do
 if str[i]=nat[j] then
 fl:=true;
 if fl then begin
 bigmas[k,l]:=str[i]; inc(l);
 end; else begin
 lengths[k]:=l;
 inc(k); l:=1;
 end;
 end;
 for i:=1 to k do
 if m<lengths[i] then begin
 m:=lengths[i];
 l:=i;end;
 for i:=1 to lengths[l] do
 write(bigmas[l,i]);
 writeln;
 end.