#include "bits/stdc++.h"
using namespace std;


int main() {
	int N;
	cin >> N;
	vector<int> V(N,0);
	for(int i=0; i<N; i++) cin >> V[i];

	vector<int> dp(N+1,0);
	dp[0] = 0;
	for (int i = 0; i < N; i++) {
		if (i == 0) {
			dp[i+1] = V[i];
			continue;
		}
		dp[i+1] = max(dp[i], dp[i-1]+V[i]);
	}
	cout << dp[N] << endl;
}