import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int[] v = new int[N];
    for(int i = 0; i < N; i++) {
      v[i] = sc.nextInt();
    }
    // dp[i]は最後の寿司が寿司iの場合の美味しさの最大値を表す
    int[] dp = new int[N];
    // max[i] = max(0≦j≦i)dp[j]
    int[] max = new int[N];
    dp[0] = v[0];
    max[0] = dp[0];
    if(N > 1) {
      dp[1] = v[1];
      max[1] = Math.max(max[0], dp[1]);
    }
    for(int i = 2; i < N; i++) {
      dp[i] = v[i] + max[i - 2];
      max[i] = Math.max(dp[i], max[i - 1]); 
    }
    System.out.println(max[N - 1]);
  }
}