#include <bits/stdc++.h>
using namespace std;
int dp[105][105][105][2];
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "{";
  typename vector<T>::const_iterator it;
  for (it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) os << ", ";
    os << *it;
  }
  return os << "}";
}
template <typename F, typename S>
ostream &operator<<(ostream &os, const map<F, S> &v) {
  os << "[";
  typename map<F, S>::const_iterator it;
  for (it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) os << ", ";
    os << it->first << " = " << it->second;
  }
  return os << "]";
}
void code();
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  code();
  return 0;
}
void code() {
  long long n;
  cin >> n;
  long long o = ceil(n / 2.0);
  long long e = n / 2;
  vector<long long> a(105);
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
  }
  memset(dp, 0x3f, sizeof(dp));
  dp[0][0][0][0] = dp[0][0][0][1] = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j <= o; j++) {
      for (int k = 0; k <= e; k++) {
        if (a[i] == 0) {
          if (k > 0)
            dp[i][j][k][0] =
                min(dp[i - 1][j][k - 1][1] + 1, dp[i - 1][j][k - 1][0]);
          if (j > 0)
            dp[i][j][k][1] =
                min(dp[i - 1][j - 1][k][0] + 1, dp[i - 1][j - 1][k][1]);
        } else {
          if (a[i] % 2 == 0) {
            if (k > 0) {
              dp[i][j][k][0] =
                  min(dp[i - 1][j][k - 1][0], dp[i - 1][j][k - 1][1] + 1);
            }
          } else {
            if (j > 0) {
              dp[i][j][k][1] =
                  min(dp[i - 1][j - 1][k][0] + 1, dp[i - 1][j - 1][k][1]);
            }
          }
        }
      }
    }
  }
  cout << min(dp[n][o][e][0], dp[n][o][e][1]) << endl;
}
