#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

int main() {
	int N;
	cin >> N;
	vector<int> V(N), dp(N);
	for (int& i : V) cin >> i;
	dp[0] = V[0];
	if (1 != N) dp[1] = max(V[0], V[1]);
	for (int i = 2; i < N; ++i) dp[i] = max(V[i] + dp[i - 2], dp[i - 1]);
	cout << dp.back();
}