import java.io.*;
import java.util.StringTokenizer;

class Main{

static final PrintWriter out=new PrintWriter(System.out);

public static void main(String[] args) throws IOException{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
String line="";
while((line=br.readLine())!=null&&!line.isEmpty()){
int n=Integer.parseInt(line);
int[] dp=new int[n+2];
int[] v=new int[n];
StringTokenizer st=new StringTokenizer(br.readLine());
for(int i=0;i<n;i++) v[i]=Integer.parseInt(st.nextToken());
for(int i=n-1;i>=0;i--){
dp[i]=Math.max(dp[i+1],dp[i+2]+v[i]);
}
out.println(dp[0]);
out.flush();
}
}
}