#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using T = tuple<int, int, int>;
#define al(a) a.begin(), a.end()
#define ral(a) a.rbegin(), a.rend()
#define sz(a) (int)a.size()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define db(a, b) cout << #a << ": " << a << " " << #b << ": " << b << endl;

int main() {
  int n;
  cin >> n;
  vector<int> a(n);
  rep(i, n) cin >> a[i];

  const int INF = 1001001001;
  vector dp(n + 1, vector<int>(2, -INF));
  auto chmax = [&](int &a, int b) { a = max(a, b); };
  dp[0][0] = 0;
  rep(i, n) rep(j, 2) {
    if (!j) chmax(dp[i + 1][1], dp[i][j] + a[i]);
    chmax(dp[i + 1][0], dp[i][j]);
  }
  int ans = max(dp[n][0], dp[n][1]);
  cout << ans << endl;
  return 0;
}