import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
	public static void main(String[] args) {
	      BufferedReader stdReader =new BufferedReader(new InputStreamReader(System.in));
	      try {
		      int N = Integer.parseInt(stdReader.readLine());
		      String[] temps = stdReader.readLine().split(" ");
		      int[] nums = new int[N];
		      for(int i=0;i<N;i++){
		    	  nums[i] = Integer.parseInt(temps[i]);
		      }
		      
		      int[] dp = new int[N];
		      if(N == 1){
		    	  System.out.println(nums[0]);
		      }else{
		    	  dp[0] = nums[0];
		    	  dp[1] = Math.max(nums[0], nums[1]);
 		    	  int max = 0;
	 		      for(int i=2;i<N;i++){
			    	  dp[i] = Math.max(dp[i-1], dp[i-2]+nums[i]);
			      }
	 		      System.out.println(dp[N-1]);
		      }
	    	  } catch (IOException e) {
			e.printStackTrace();
	      }
	}	
}