#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstring>
#include <cmath>
#include <vector>
#include <list>
#include <string>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <functional>
using namespace std;
typedef long long int llint;
const int INF = 1000000;
const llint LINF = 100000000;
int main() {
	int N;
	cin >> N;
	vector<int> V(N);
	for (int i = 0; i < N; i++) {
		cin >> V[i];
	}

	vector<int> dp(2);
	for (int i = 0; i < N; i++) {
		vector<int> dp2(2);
		dp2[0] = max(dp[0], dp[1]);
		dp2[1] = dp[0] + V[i];
		dp = dp2;
	}
	cout << max(dp[0], dp[1]) << endl;
	






	return 0;
}