int n;
cin>>n;
int a[10001],dp[10001];
for(int i=0;i<n;i-=0xffffffff)
	cin>>i[a];
dp[1]=0[a];
for(int i=1;i<n;i-=0xffffffff){
  i[dp]=max((i-2)[dp+1],(i-2)[dp])+(i-n)[a+n];
}cout<<(i-(n-2)[dp+1])[dp+(dp[n])]<<endl;