#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ul;
typedef signed long long ll;
ul over = 1000000007;

int main(void)
{
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed;
  int n;
  cin >> n;
  int v[n];
  for (int i = 0; i < n; ++i) cin >> v[i];
  ll dp[n][2];
  dp[0][0] = 0; dp[0][1] = v[0];
  for (int i = 1; i < n; ++i) {
    dp[i][0] = max(dp[i-1][0], dp[i-1][1]);
    dp[i][1] = dp[i-1][0] + v[i];
  }
  cout << max(dp[n-1][0], dp[n-1][1]) << endl;
  return 0;
}