#include<bits/stdc++.h>
using namespace std;
int a[51],f[51],n,i;
int main(){
    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: liyunshuo
	Language: C++
	Result: Accepted
	Time:32 ms
	Memory:2072 kb
****************************************************************/