#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n;
	cin>>n;
	vector<int> arr(n);
	for(int i = 0;i<n;i++) 
	{
		cin>>arr[i];
	}
	vector<int> dp(n);
	dp[0] = arr[0];
	dp[1] = max(arr[0],arr[1]);
	for(int i = 2;i<n;i++)
	{
		dp[i] = max(dp[i-1] , dp[i-2] + arr[i]);
	}
	cout<<dp[n-1]<<endl;
}