#include <algorithm>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using namespace std;

typedef long long ll;

#define MOD 1000000007

int main() {
  int n;
  cin >> n;
  vector<int> v(n + 1);
  for (int i = 1; i <= n; ++i) {
    cin >> v[i];
  }
  vector<vector<int> > dp(n + 1, vector<int>(2));
  for (int i = 1; i <= n; ++i) {
    dp[i][0] = max(dp[i][0], max(dp[i - 1][0], dp[i - 1][1]));
    dp[i][1] = max(dp[i][1], dp[i - 1][0] + v[i]);
  }
  cout << max(dp[n][0], dp[n][1]) << endl;
  return 0;
}