#include<iostream>
#include<string>
#include<string.h>
#include<algorithm>
#include<stdio.h>
#include<cmath>
#include<vector>
#include<utility>
#include<stack>
#include<queue>
#include<list>
#include<bitset>

#define FOR(i, a, b) for(int i=(a);i<=(b);i++)
#define RFOR(i, a, b) for(int i=(a);i>=(b);i--)
#define MOD 1000000007
#define INF 1000000000

using namespace std;


int main(void) {
	int n;
	int v[1001];
	int dp[1001];

	cin >> n;
	FOR(i, 1, n) {
		cin >> v[i];
	}

	dp[1] = v[1];
	dp[2] = max(v[1], v[2]);
	FOR(i, 3, n) {
		dp[i] = max(dp[i - 1], dp[i - 2] + v[i]);
	}
	cout << dp[n] << endl;
	return 0;
}