var f,g:text;
    a,b:array[-10..100000]of byte;
    n,i,j,sol:longint;
function max(a,b:longint):longint;
begin
        if a>b then max:=a
                else
                        max:=b;
end;
begin
        assign(f,'oo.in');
        reset(f);
        readln(f,n);
        for i:=1 to n do
                read(f,a[i]);
        close(f);
        for i:=0 downto -10 do
                a[i]:=a[n+1];
        sol:=-maxlongint;
        for i:=3 downto 1 do begin
                for j:=i to n-3+i do
                        b[j]:=max(b[j-1],b[j-3]+a[j-1]+a[j]);
                sol:=max(sol,b[i]);
                end;
        assign(g,'oo.out');
        writeln(g);
        writeln(g,sol);
        close(g);
end.