import java.util.*;

class Main{
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] v = new int[n+1];
		int[] dou = new int[n+1];
		Arrays.fill(dou,-1);
		for(int i = 1; i <= n; i++){
			v[i] = sc.nextInt();
		}
		class Inner{
			public int umai(int mai){
				if(dou[mai] == -1){
					if(mai >= 3){
						dou[mai] = Math.max(umai(mai-2) + v[mai],umai(mai-3) + v[mai]);
						return dou[mai];
					}else if(mai >= 2){
						dou[mai] = umai(mai-2) + v[mai];
						return dou[mai];
					}else{
						dou[mai] = v[mai];
						return dou[mai];
					}
				}else{
					return dou[mai];
				}
			}
		}
		Inner in = new Inner();
		int answer = Math.max(in.umai(n),in.umai(n-1));
		System.out.print(answer);
	}
}