#include <iostream>
#include <map>
#include <set>
#include <list>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>
#include <string>
#include <vector>
#include <complex>
#include <cstdlib>
#include <cstring>
#include <numeric>
#include <sstream>
#include <algorithm>
#include <functional>
#include <limits.h>
#include <bitset>

#include <tuple>
#include <unordered_map>

#define mp       make_pair
#define mt       make_tuple
#define pb       push_back
#define rep(i,n) for(int i=0;i<(n);i++)

using namespace std;

typedef    long long          ll;
typedef    unsigned long long ull;
typedef    pair<int,int>      pii;

const int INF=1<<29;
const double EPS=1e-9;

const int dx[]={1,0,-1,0},dy[]={0,-1,0,1};
int N;
vector<int> V;
int dp[1010];
int memo(int pos){
	if (pos >= N){
		return 0;
	}
	if (dp[pos] >= 0){
		return dp[pos];
	}
	int res = 0;
	res = max(res, memo(pos + 2) + V[pos]);
	res = max(res, memo(pos + 1));
	return dp[pos] = res;
}
int main(){
	cin >> N;
	for (int i = 0; i < N; i++){
		int x;
		cin >> x;
		V.push_back(x);
	}
	memset(dp, -1, sizeof(dp));
	cout << memo(0) << endl;
	return 0;
}