package backjoon;

// https://www.acmicpc.net/problem/2156

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

public class _2156 {

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

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

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

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

int[] dp = new int[N+1];

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

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

}

dp[1] = arr[1];

if (N > 1) {

dp[2] = arr[1] + arr[2];

}

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

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

}

System.out.println(dp[N]);

}

}

/*

input

6

6

10

13

9

8

1

output

33

*/