#include<bits/stdc++.h>
using namespace std;
int a[51],dp[51],n,i;
int main(){
    cin>>n;
    for(i=1;i<=n;i++) cin>>a[i];
    dp[1]=a[1];
    dp[2]=a[2];
    for(i=3;i<=n;i++) dp[i]=max(dp[i-2],dp[i-3])+a[i];
    cout<<max(dp[n-1],dp[n]);
    return 0;
}
/**************************************************************
	Problem: 1653
	User: zhengyuxuan
	Language: C++
	Result: Accepted
	Time:23 ms
	Memory:2072 kb
****************************************************************/