#include <bits/stdc++.h>
using namespace std;
long long L[100005], R[100005], odd[100005], s[100005], dp[100005], ans = 0;
int n;
int main() {
  scanf("%d", &n);
  for (int i = 1; i < n; i++) scanf("%I64d", &s[i]);
  L[0] = 0;
  for (int i = 1; i < n; i++) {
    if (s[i] == 1)
      L[i] = 0;
    else
      L[i] = L[i - 1] + s[i] / 2 * 2;
  }
  R[n - 1] = 0;
  for (int i = n - 2; i >= 0; i--) {
    if (s[i + 1] == 1)
      R[i] = 0;
    else
      R[i] = R[i + 1] + s[i + 1] / 2 * 2;
  }
  dp[0] = 0;
  for (int i = 1; i < n; i++) {
    dp[i] = max(dp[i - 1] + (s[i] - 1) / 2 * 2 + 1, L[i]);
  }
  for (int i = 0; i < n; i++) {
    ans = max(ans, dp[i] + R[i]);
  }
  printf("%I64d\n", ans);
  return 0;
}
