program Project2;

{$APPTYPE CONSOLE}

uses
  SysUtils;

const
  MAXIN = 10000;

var
  n, p, i, j, z, j1, j2, i1, i2: integer;
  s: string;
  a: array [1..MAXIN, 1..MAXIN] of integer;

begin
  readln(n);

  for i := 1 to n do
  begin
    readln(s);
    j := 1;
    z := 1;
    while j <= length(s) do
    begin
      a[i][z] := strtoint(s[j]) * 10 + strtoint(s[j + 1]);
      inc(z);
      inc(j, 2);
    end;
  end;

  i1 := 1;
  i2 := n;
  j1 := 1;
  j2 := n;

  for p := 1 to n div 2 + 1 do
  begin
    for j := j1 to j2 do
      write(char(a[i1][j] + 96));
    dec(j2);
    for i := i1 to i2 do
      write(char(a[i][j2] + 96));
    dec(i2);
    for j := j2 downto j1 do
      write(char(a[i2][j] + 96));
    inc(j1);
    for i := i2 downto i1 do
      write(char(a[i][j1] + 96));
    inc(i1);
  end;
  readln;
  readln;
end.