#include<iostream>
#include<algorithm>
using namespace std;
int dp[1010];
int main(){
	int N, V[1010];
	cin >> N;
	for (int i = 1; i <= N; i++)cin >> V[i];
	dp[0] = 0; dp[1] = V[1];
	for(int i=2;i<=N;i++)dp[i] = max(dp[i-1], dp[i-2] + V[i]);
	cout << dp[N]<<endl;
	return 0;
}