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