#include<bits/stdc++.h>
using namespace std;
int a[51],f[51];
int main(){
	int n,i;
	cin>>n;
	for(i=1;i<=n;i++){
		cin>>a[i];
	}
	f[1] = a[1];
	f[2] = a[2];
	for(i=3;i<=n;i++){
		f[i] = max(f[i-2],f[i-3]) + a[i];
	}
	cout<<max(f[n-1],f[n]);
	return 0;
}

/**************************************************************
	Problem: 1653
	User: admin
	Language: C++
	Result: Accepted
	Time:21 ms
	Memory:2072 kb
****************************************************************/