Untitled

uses crt;
var i,n,ans:longint;
    x:byte;
    a:array[1..4] of longint;
procedure Enter;
begin
        readln(n);
        for i:=1 to n do
        begin
                read(x);
                inc(a[x]);
        end;
        readln;
end;
procedure Gop1voi3;
begin
        inc(ans,a[3]);
        dec(a[1],a[3]);
end;
procedure Gop2voi2;
begin
        inc(ans,a[2] div 2);
        a[2]:=a[2] mod 2;
end;
procedure Gop1voi2;
begin
        if a[2]>0 then   
        begin
                inc(ans);
                dec(a[1],2);
        end;
        if a[1]>0 then
        begin
                inc(ans,a[1] div 4);
                if a[1] mod 4 <> 0 then inc(ans);
        end;
end;
begin
        clrscr;
        Enter;
        //for i:=1 to 4 do write(a[i],' ');
        ans:=a[4];
        Gop1voi3;
        Gop2voi2;
        Gop1voi2;
        write(ans);
        readln
end.