var
n:integer;
s:array[1..8]of ansistring;
g:array[1..8]of integer;
ans:ansistring;

  procedure mj(w:longint;st:ansistring);
  var
  i:longint;
  a:ansistring;
  begin
  if w<>n then
  for i:=1 to n do
  if g[i]=0 then
    begin
    g[i]:=1;
    mj(w+1,st+s[i]);
    g[i]:=0;
    end;
  if w=n then
  if (ans='')or(ans>st) then ans:=st;
  end;

begin
assign(input,'substring.in');
assign(output,'substring.out');
reset(input);
rewrite(output);

readln(n);
for n:=1 to n do
readln(s[n]);

mj(0,'');
writeln(ans);

close(input);close(output);
end.