var f,g:text;
a,s1,s2:array[1..100000] of integer;
n,i,j,k:longint;
function max(x,y:longint):longint;
var k:longint;begin
if x>y then k:=y
        else k:=x;
end;
begin
assign(f,'oo.in');
assign(g,'oo.out');
reset(F);
rewrite(G);
readln(f,n);
for i:=1 to n do
        read(a[i]);
if i=2 then writeln(g,a[1]+a[2])
else
begin
s1[1]:=0;
s1[2]:=a[1]+a[2];
for j:=4 to n-2 do
         s1[j+1]:=max(s1[j-2]+a[j]+a[j+1],s1[j-3]+a[j]+a[j+1]);
s2[1]:=0;
s2[2]:=0;
s2[3]:=a[2]+a[3];
for j:=5 to n-1 do
        s2[j+1]:=max(s2[j-2]+a[j]+a[j+1],s2[j-3]+a[j]+a[j+1]);
writeln(g,max(s1[n-1],s2[n]));end; close(F);close(G);
end.