#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define coutf(f) cout << fixed << setprecision(f)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()

int main() {
	int n;
	cin >> n;
	vector<int> v(n), s(n + 1, 0);
	rep(i, n) cin >> v[i];
	s[1] = v[0];
	for (int i = 2; i <= n; i++) s[i] = max(s[i - 1], s[i - 2] + v[i - 1]);
	cout << s[n] << endl;
	return 0;
}