#include <bits/stdc++.h>
#define REP(i,a,b) for(ll i=(a);i<(b);i++)
#define RREP(i,a,b) for(int i=(a);i>=(b);i--)
#define pq priority_queue
#define P pair<int,int>
#define P2 pair<int,P>
#define P3 pair<int,P2>
typedef long long ll; typedef long double ld;
using namespace std;
const int INF=1e9, MOD=1e9+7, around[]={0,1,1,-1,-1,0,-1,1,0,0};
const ll LINF=1e18;
const ld PI=abs(acos(-1));
int n,a;
int dp[1010];

int main(){
	cin >> n;
	
	REP(i,0,n){
		cin >> a;
		if(i==0) dp[i]=a;
		else if(i==1) dp[i]=max(dp[i-1],a);
		else dp[i]=max(dp[i-1],dp[i-2]+a);
	}
	
	cout << dp[n-1] << endl;
	return 0;
}