#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <iomanip>
using namespace std;
#define INF 1e9
#define PI acos(-1)
typedef long long ll;

int dp[1001];

int main() {
	
	int n;
	cin >> n;
	vector<int> value(n);
	for (int i = 0; i < n; i++)cin >> value[i];

	dp[0] = 0; dp[1] = value[0];
	for (int i = 2; i <= n; i++) {
		dp[i] = max(dp[i-1],dp[i - 2] + value[i-1]);
	}

	cout << dp[n] << endl;

	return 0;
}