program mafandejucan;
var
  f:array[1..30000,1..3]of longint;
  i,j,k,n,min,m:longint;
  d:array[1..30000]of integer;
begin
  assign (input,'egroup.in');
  reset (input);
    readln (n);
    for i:=1 to n do
      readln (d[i]);
  close (input);
  for i:=1 to 3 do
    if i=d[1] then
      f[1,i]:=0
    else
      f[1,i]:=1;
  for i:=2 to n do
    for j:=1 to 3 do
    begin
      min:=maxlongint;
      if j=d[i] then
        for k:=1 to j do
          if f[i-1,k]<min then
            min:=f[i-1,k];
      if j<>d[i] then
        for k:=1 to j do
          if f[i-1,k]+1<min then
            min:=f[i-1,k]+1;
      f[i,j]:=min
    end;
  m:=maxlongint;
  for i:=1 to 3 do
    if f[n,i]<maxlongint then
      m:=f[n,i];
  for i:=1 to 3 do
    if i=d[1] then
      f[1,i]:=0
    else
      f[1,i]:=1;
  for i:=2 to n do
    for j:=1 to 3 do
    begin
      min:=maxlongint;
      if j=d[i] then
        for k:=3 downto j do
          if f[i-1,k]<min then
            min:=f[i-1,k];
      if j<>d[i] then
        for k:=3 downto j do
          if f[i-1,k]+1<min then
            min:=f[i-1,k]+1;
      f[i,j]:=min
    end;
  for i:=1 to 3 do
    if f[n,i]<m then
      m:=f[n,i];
  assign (output,'egroup.out');
  rewrite (output);
    writeln (m);
  close (output)
end.