#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 = 1 << 30;
const ll INFL = 1LL<<60;
const ll mod = 1000000007;		





int main() {
	int n;
	cin >> n;
	VI v(n);
	REP(i, n)cin >> v[i];

	VI dp(n + 10);
	dp[0] = 0;
	dp[1] = v[0];
	REP(i, n - 1) {
		dp[i + 2] = max(dp[i + 1], dp[i] + v[i + 1]);
	}

	cout << dp[n] << endl;
	return 0;
}