program sieutrom;
uses crt;
var i,n:longint;
f1,f2:text;
a,b,f:array[0..1000000] of longint;
function max(a,b:longint):longint;
begin
if a>b then exit(a) else exit(b);
end;
begin
assign(f1,'sieutrom.inp');reset(f1);
assign(F2,'sieutrom.out');rewrite(f2);
readln(f1,n);
for i:=1 to n do
read(f1,a[i]);
b[1]:=a[1]; f[1]:=a[1]+a[2];
for i:=2 to n do
begin
b[i]:=max(b[i-2]+a[i],f[i-1]);
f[i]:=a[i]+a[i+1];
end;
writeln(f2,b[n]);
close(f1);
close(f2);
end.