#include <bits/stdc++.h>
using namespace std;

using i64 = long long;
using u64 = unsigned long long;
using u32 = unsigned;

using u128 = unsigned __int128;
using i128 = __int128;


void solve(){
	int n;cin>>n;
	vector<int> a(n+1);
	for(int i=1;i<=n;++i){cin>>a[i];}
	if(n==1){
		cout<<a[1];return;
	}
	
	vector<int> b(n+1,0);
	b[1]=a[1];
	for(int i=2;i<=n;++i){
		b[i]=max(b[i-1],a[i]+b[i-2]);
	}
	cout<<b[n];
	return;
}


int main(){
	ios::sync_with_stdio(false);cin.tie(nullptr);
	
		solve();
	
	return 0;
}


















/*
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