#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
#define REP(i,n) for(int i=0; i<int(n); i++)
#define FOR(i,m,n) for(int i=int(m); i<int(n); i++)
#define ALL(obj) (obj).begin(),(obj).end()
#define VI vector<int>
#define VLL vector<long long>
#define VVI vector<vector<int>>
#define VVLL vector<vector<long long>>
#define VC vector<char>
#define VS vector<string>
#define VVC vector<vector<char>>
#define fore(i,a) for(auto &i:a)

typedef pair <int, int> P;
template<class T> bool chmax(T &a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> bool chmin(T &a, T b) { if (a > b) { a = b; return true; } return false; }
const int  INF = 2147483647;
const ll INFL = 9223372036854775807;
const ll mod = 1000000007;





int main() {
	
	int n;
	cin >> n;
	VI v(n);
	REP(i, n)cin >> v[i];
	if (n == 1) {
		cout << v[0] << endl;
		return 0;
	}
	if (n == 2) {
		cout << max(v[0], v[1]) << endl;
		return 0;
	}
	VI dp(10000, 0);
	dp[0] = v[0], dp[1] = v[1], dp[2] = v[2];
	FOR(i, 3, n) {

		dp[i] = max({ dp[i - 1], dp[i - 2] + v[i], dp[i - 3] + v[i] });
	}

	cout << dp[n-1] << endl;

	
	


	return 0;
}