#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cstring>
#include <climits>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;
 
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };
 
ll MOD = 1000000007;

int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, -1, 0, 1};

int main() {
	int N; cin >> N;
	vector<int> V(N + 10);
	for (int i = 1; i <= N; i++) cin >> V[i];
	vector<int> dp(N + 10);
	dp[1] = V[1];
	for (int i = 0; i <= N; i++) {
		dp[i + 1] = max(dp[i + 1], dp[i]);
		dp[i + 2] = max(dp[i + 2], dp[i] + V[i + 2]);
	}
	cout << dp[N] << endl;
}