var f,g:text;
a:array[1..100000] of longint;
sum1,sum2:array[1..100000] of longint;
n,i,j,k,l:longint;
function max(a,b:longint):longint;
var x:longint;
begin
if a>b then x:=a
        else x:=b;
max:=x;
end;
begin
assign(f,'oo.in');
reset(F);
assign(g,'oo.out');
rewrite(G);
readln(f,n);
for i:=1 to n do read(f,a[i]);
sum1[1]:=0;
sum1[2]:=a[1]+a[2];
sum1[3]:=sum1[1];
for i:=3 to n-2 do
        sum1[i+1]:=max(max(sum1[i-2]+a[i]+a[i+1],sum1[i-1]),sum1[i]);
sum2[1]:=0;
sum2[2]:=0;
sum2[3]:=a[2]+a[3];
sum2[4]:=sum2[3];
for i:=4 to n-1 do
        sum2[i+1]:=max(max(sum2[i-2]+a[i]+a[i+1],sum2[i-1]),sum2[i]);
writeln(g,max(sum1[n-1],sum2[n]));
close(F);
close(G);
end.