#include<cstdio>
#include <iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>

#define mod 1000000007;

using namespace std;
typedef long long ll;
typedef pair<ll, ll> Pr;

ll dp[1010];
ll v[1010];

int main()
{
	int N;
	cin >> N;
	for (int i = 0; i < N; i++)
		cin >> v[i];

	dp[0] = v[0];
	dp[1] = max(v[0], v[1]);

	for (int i = 1; i < N; i++) {
		dp[i + 1] = max(dp[i],dp[i-1]+v[i+1]);
	}

	cout << dp[N] << endl;

	return 0;
}