记录编号	79612	评测结果	AWWAAAAWAWA
题目名称	[USACO Feb08] 麻烦的聚餐	最终得分	63
用户昵称	Alan	是否通过	未通过
代码语言	Pascal	运行时间	0.010 s
提交时间	2013-11-05 23:27:58	内存使用	0.50 MiB

var
  b:array[-1..30010]of integer;
  a:array[-1..30010,0..4]of integer;
  l,n,i,j,max:integer;
begin
  assign(input,'egroup.in');
  assign(output,'egroup.out');
  reset(input);
  rewrite(output);

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

  for j:=1 to 3 do
    if b[1]=j then
      a[1,j]:=0
    else
      a[1,j]:=1;
  for i:=2 to n do
    for j:=1 to 3 do
      begin
        a[i,j]:=30001;
          if b[i]=j then
            begin
              if (j-1<1) or (a[i-1,j-1]>=a[i-1,j]) then
                l:=a[i-1,j]
              else l:=a[i-1,j-1];
              if l<a[i,j] then a[i,j]:=l;
            end
          else
            begin
              if (j-1<1) or (a[i-1,j-1]>=a[i-1,j]) then
                l:=a[i-1,j]+1
              else l:=a[i-1,j-1]+1;
              if l<a[i,j] then a[i,j]:=l;
            end;
      end;

      max:=a[n,3];

  for j:=1 to 3 do
    if b[n]=j then
      a[n,j]:=0
    else
      a[n,j]:=1;

  for i:=n-1 downto 1 do
    for j:=1 to 3 do
      begin
        a[i,j]:=30001;
          if b[i]=j then
            begin
              if (j-1<1) or (a[i+1,j-1]>=a[i+1,j]) then
                l:=a[i+1,j]
              else
                l:=a[i+1,j-1];
              if l<a[i,j] then a[i,j]:=l;
            end
          else
            begin
              if (j-1<1) or (a[i+1,j-1]>=a[i+1,j]) then
                l:=a[i+1,j]+1
              else
                l:=a[i+1,j-1]+1;
              if l<a[i,j] then a[i,j]:=l;
            end;
      end;

  if max>a[1,3] then
    max:=a[1,3];

  writeln(max);

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