#include <bits/stdc++.h>
using namespace std;
const long long md = 1e9 + 7;
const long long MX = 2e5 + 5;
const long long INF = 1e18;
const long double PI = 4 * atan((long double)1);
long long power(long long a, long long n) {
  long long res = 1;
  while (n) {
    if (n % 2) res = (res % md * a % md) % md;
    a = (a % md * a % md) % md;
    n /= 2;
  }
  res %= md;
  return res;
}
long long abst(long long a) { return ((a < 0) ? (-1 * a) : (a)); }
class cmp_set {
 public:
  bool operator()(long long a, long long b) { return a > b; }
};
long long arr[105], dp[105][105][105][3];
long long n;
long long fun(long long i, long long e, long long o, long long prev) {
  if (i == (n + 1)) return 0;
  if (dp[i][e][o][prev] != -1) return dp[i][e][o][prev];
  long long res = 1e15;
  if (arr[i] != 0) {
    if (prev != 2 && arr[i] % 2 != prev)
      res = fun(i + 1, e, o, arr[i] % 2) + 1;
    else
      res = fun(i + 1, e, o, arr[i] % 2);
  } else {
    if (prev == 2) {
      if (e > 0) res = min(res, fun(i + 1, e - 1, o, 0));
      if (o > 0) res = min(res, fun(i + 1, e, o - 1, 1));
    } else {
      if (e > 0) res = min(res, fun(i + 1, e - 1, o, 0) + (prev == 1));
      if (o > 0) res = min(res, fun(i + 1, e, o - 1, 1) + (prev == 0));
    }
  }
  return dp[i][e][o][prev] = res;
}
int32_t main() {
  cin >> n;
  memset(dp, -1, sizeof(dp));
  long long oc = 0, ec = 0;
  map<long long, long long> mp;
  for (long long i = 1; i <= n; i++) {
    cin >> arr[i];
    mp[arr[i]]++;
  }
  for (long long i = 1; i <= n; i++) {
    if (mp.count(i) == 0) {
      if (i % 2)
        oc++;
      else
        ec++;
    }
  }
  long long res = fun(1, ec, oc, 2);
  cout << res << "\n";
  return 0;
}
