var a:array[1..1000] of integer;
    f:array[1..2,0..1000,0..30] of integer;
    t,w,i,j,ans:integer;

function max(a,b:longint):longint;

  begin
    if a>b then exit(a) else exit(b);
  end;

begin
  readln(t,w);
  for i:=1 to t do
    readln(a[i]);
  fillchar(f,sizeof(f),0);
  for i:=0 to w do
    f[2,0,i]:=-30000;
  ans:=0;
  for i:=1 to t do
    for j:=0 to w do
      begin
        if j>0 then
          f[a[i],i,j]:=max(f[a[i],i-1,j],f[3-a[i],i-1,j-1])+1
        else
          f[a[i],i,j]:=f[a[i],i-1,j]+1;
        f[3-a[i],i,j]:=f[3-a[i],i-1,j];
        ans:=max(ans,f[a[i],i,j]);
      end;
  writeln(ans);
end.