#include "bits/stdc++.h"
using namespace std;
#define REP(i,a) for(int i = 0; i < (a);i++)
#define ALL(a) (a).begin(),(a).end()
typedef long long ll;
typedef pair<int, int> P;
const int INF = 1e9;
const int MOD = 1e9 + 7;
using Graph = vector < vector<int>>;
long int sum[200020] = {};
int main() {
	int n;
	cin >> n;
	vector<int> s(1020,0);
	vector<int>	dp(1020,0);
	for (int i = 0; i < n; i++) {
		int a;
		cin >> a;
		s[i] = a;
	}
	dp[0] = s[0];
	dp[1] = max(s[1],s[0]);
	for (int i = 2; i < n; i++) {
		dp[i] = max(dp[i - 1], dp[i - 2] + s[i]);
	}
	cout << dp[n-1];
}