var a,v:Array[-10..100100] of longint;
    f,g:Text;
    rez,i,n,k:longint;

function max(x,y:longint):longint;
 begin
        if x>y then max:=x
        else max:=y;
 end;

begin
 assign(f,'oo.in'); reset(f);
 assign(g,'oo.out'); rewrite(g);
 read(f,n);
 for i:=1 to n do
        read(f,a[i]);
 for i:=0 downto -10 do
        a[i]:=a[n+i];
 rez:=-maxlongint;
 for k:=3 downto 1 do begin
        for i:=k to n-3+k do
                v[i]:=max(v[i-1],v[i-3]+a[i-1]+a[i]);
        rez:=max(rez,v[i]);
 end;
 writeln(g,rez);
 close(f); close(g);
end.