Pascal :

var
a,b:array[0..300000] of longint;
i,j,k,n,m,tot:longint;
c:char;
procedure deal(x,y:longint);
var i,j:longint;
begin
 if x>y then exit;
 if x=y then begin inc(tot); b[tot]:=a[x]; exit; end;
 i:=x; j:=y;
 if a[x]<a[y] then
 begin
  inc(tot);
  b[tot]:=a[x];
  deal(x+1,y);
  exit;
 end;
 if a[x]>a[y] then
 begin
  inc(tot);
  b[tot]:=a[y];
  deal(x,y-1);
  exit;
 end;
 while (a[i]=a[j])and(i+1<=j-1) do
 begin
  inc(i);
  dec(j);
 end;
 if a[i]>=a[j] then
 begin
  inc(tot);
  b[tot]:=a[y];
  deal(x,y-1);
  exit;
 end;
 if a[i]<a[j] then
 begin
  inc(tot);
  b[tot]:=a[x];
  deal(x+1,y);
  exit;
 end;
end;
begin

 readln(n);
 for i:=1 to n do
 begin
  readln(c);
  a[i]:=ord(c)-ord('A');
 end;
 deal(1,n);
 for i:=1 to n do
  if i mod 80=0 then
   writeln(chr(b[i]+ord('A')))
    else write(chr(b[i]+ord('A')));

end.