#include <iostream>
#include<vector>
#include<string>
#include<algorithm>
#include<iomanip>
#include<map>
#include<stack>
#include<queue>
#include<set>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define req(i,n) for(int i = 1;i <=  n; i++)
#define rrep(i,n) for(ll i = n-1;i >= 0;i--)
#define ALL(obj) begin(obj), end(obj)
#define RALL(a) rbegin(a),rend(a)
typedef long long ll;
typedef long double ld;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const ll INF = 1e18;
ll mod = 1e9 + 7;
int main() {
	int n; cin >> n; vector<int> v(n+1,0);
	req(i, n) cin >> v[i];
	vector<int> dp(n + 10, 0);
	req(i, n) {
		if (i != 1) chmax(dp[i], dp[i - 2] + v[i]);
		else dp[i] = v[i];
		chmax(dp[i + 1], dp[i]);
	}cout << dp[n] << endl;
}