#include <stdio.h>
#include <iostream>
#include <string>
using namespace std;

int main(){
	
	int n;
	cin >> n;

	int before_2 = 0;
	int before_1 = 0;
	int ans = 0;

	for(int i=0; i<n; i++){
		int v;
		cin >> v;

		if(v+before_2 > before_1){
			ans = v+before_2;
		}
		else{
			ans = before_1;

		}

		before_2 = before_1;
		before_1 = ans;
	}

	cout << ans << endl;

	return 0;
}