#include <iostream>
#include <sstream>
#include <vector>
#include <algorithm>
#include <string>
#include <functional>
#include <numeric>
#include <ctype.h>
#include <cstdlib>
#include <string.h>
#include <cmath>
#include <cstdio>
#include <map>
#include <queue>
#include <utility>
#define rep(i, n) for(int i = 0; i < n; i++);

using namespace std;

const int INF = 1000000007;
const double PI = acos(-1.0);
typedef long long llong;

const int N = 1000;
int dp[N + 1];
int val[N];

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

	dp[0] = val[0];
	dp[1] = max(val[1], val[0]);

	for (int i = 2; i <= n; i++)
		dp[i] = max(dp[i - 1], dp[i - 2] + val[i]);

	cout << dp[n] << endl;
	

	return 0;


}