#include "bits/stdc++.h"

using namespace std;

#define FOR(i, j, k) for(int i = j; i < k; ++i)
#define rep(i, j) FOR(i, 0, j)
#define FORr(i, j, k) for(int i = j; i >= k; --i)
#define repr(i, j) FOR(i, j, 0)
#define INF INT_MAX

typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
typedef pair<P, int> Pi;

const int MOD = 1000000007;
const int dy[] = { 0, 0, 1, -1 };
const int dx[] = { 1, -1, 0, 0 };

template <class T> void chmin(T& a, const T& b) { a = min(a, b); }
template <class T> void chmax(T& a, const T& b) { a = max(a, b); }

int v[1000];
int dp[1001];


int main() {
	int n;
	scanf("%d", &n);
	rep(i, n) scanf("%d", &v[i]);
	dp[0] = 0;
	dp[1] = v[0];
	FOR(i, 2, n + 1) {
		dp[i] = max(dp[i - 1], dp[i - 2] + v[i - 1]);
	}
	printf("%d\n", dp[n]);
	return 0;
}