#include <bits/stdc++.h>
using namespace std;

#define rep(i,j,n) for(int i=j;i<n;++i)
#define all(i) i.begin(),i.end()
#define rall(i) i.rbegin(), i.rend()
#define INF 1e9
#define LINF 1e18
const int mod = 1e9 + 7;

typedef long long i64;
typedef pair<int, int> pi;

template <class T> using vt = vector<T>;
template <class T> using vvt = vector<vector<T>>;

i64 gcd(i64 n, i64 m) {return (m == 0? n : gcd(m, n % m));}
i64 lcd(i64 n, i64 m) {return (n / gcd(n, m) * m);}
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n;
  cin >> n;
  vt<int> v(n);
  rep(i, 0, n) cin >> v[i];

  vvt<int> dp(n + 1, vt<int>(2, 0));
  rep(i, 0, n) {
    dp[i + 1][0] = max(dp[i][0], dp[i][1]);
    dp[i + 1][1] = dp[i][0] + v[i];
  }
  cout << max(dp[n][0], dp[n][1]) << endl;
}