// https://www.acmicpc.net/problem/2579

public static void main(String[] args) throws IOException{

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

int n = Integer.parseInt(br.readLine());

int[] dy = new int[n + 1];

int[] arr = new int[n + 1];

for (int i = 1; i <= n; i++) {

arr[i] = Integer.parseInt(br.readLine());

}

dy[0] = 0;

dy[1] = arr[1];

if(n > 1) dy[2] = arr[2] + arr[1];

for (int i = 3; i <= n; i++) {

dy[i] = Math.max(dy[i - 2] + arr[i], dy[i - 3] + arr[i - 1] + arr[i]);

}

System.out.println(dy[n]);

}