#include <iostream>
using namespace std;
int solve(int arr[], int n)
{
	if (n == 1)
		return arr[0];
	int col[n];
	col[0] = arr[0];
	col[1] = max(arr[0], arr[1]);
	for (int i = 2; i < n; i++)
	{
		col[i] = max(col[i-1], col[i-2] + arr[i]);
		col[i] = max(col[i], arr[i]);
	}
	return col[n-1];
}
int main()
{
    int n;
    cin>>n;
    int arr[n];
    for(int i=0;i<n;i++)
        cin>>arr[i]
	cout <<solve(arr, n)<<endl;

}