#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1e+5 + 10;
long long b[MAXN], l[MAXN], r[MAXN], o[MAXN], dp[MAXN];
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n - 1; i++) {
    cin >> b[i];
  }
  for (int i = 1; i < n; i++) {
    l[i] = b[i - 1] - (b[i - 1] % 2) + l[i - 1];
    if (b[i - 1] == 1) l[i] = 0;
  }
  for (int i = n - 2; i > -1; i--) {
    r[i] = b[i] - (b[i] % 2) + r[i + 1];
    if (b[i] == 1) r[i] = 0;
  }
  for (int i = 1; i < n; i++) {
    o[i] = o[i - 1] + b[i - 1] - (b[i - 1] % 2 == 0);
  }
  long long ans = 0, m = 0;
  for (int i = 0; i < n; i++) {
    m = max(m, l[i] - o[i]);
    ans = max(ans, r[i] + o[i] + m);
  }
  cout << ans;
  return 0;
}
