#include <bits/stdc++.h>
using namespace std;
using ll = int64_t;
template <typename T, typename U>
ostream& operator<<(ostream& _s, pair<T, U> _t) {
  _s << "(" << _t.first << "," << _t.second << ")";
  return _s;
}
template <typename T, typename U>
istream& operator>>(istream& _s, pair<T, U>& _t) {
  _s >> _t.first >> _t.second;
  return _s;
}
template <typename T>
ostream& operator<<(ostream& _s, vector<T> _t) {
  for (int i = 0; i < (int)(_t.size()); i++) _s << (i ? " " : "") << _t[i];
  return _s;
}
template <typename T>
istream& operator>>(istream& _s, vector<T>& _t) {
  for (int i = 0; i < (int)(_t.size()); i++) _s >> _t[i];
  return _s;
}
template <typename T>
ostream& operator<<(ostream& _s, vector<vector<T>> _t) {
  for (int i = 0; i < (int)(_t.size()); i++) {
    _s << i << ": " << _t[i] << endl;
  }
  return _s;
}
const int INF = 1000;
const int N = 110;
int dp[N][N][N][2];
void improve(int& a, int b) { a = min(a, b); }
int main() {
  ios_base::sync_with_stdio(false);
  int n;
  cin >> n;
  int odds = (n + 1) / 2, evens = n / 2;
  vector<int> a(n);
  cin >> a;
  for (int i = 0; i < (int)(n); i++) {
    if (a[i]) {
      if (a[i] % 2)
        odds--;
      else
        evens--;
    }
  }
  for (int i = 0; i < (int)(N); i++)
    for (int j = 0; j < (int)(N); j++)
      for (int k = 0; k < (int)(N); k++) {
        dp[i][j][k][0] = INF;
        dp[i][j][k][1] = INF;
      }
  dp[0][odds][evens][0] = 0;
  dp[0][odds][evens][1] = 0;
  for (int pos = 0; pos < (int)(n); pos++) {
    for (int o = 0; o < (int)(n + 1); o++)
      for (int e = 0; e < (int)(n + 1); e++) {
        for (int last = 0; last < (int)(2); last++) {
          if (dp[pos][o][e][last] == INF) continue;
          if (a[pos] == 0) {
            if (o > 0) {
              improve(dp[pos + 1][o - 1][e][1],
                      dp[pos][o][e][last] + (last == 0));
            }
            if (e > 0) {
              improve(dp[pos + 1][o][e - 1][0],
                      dp[pos][o][e][last] + (last == 1));
            }
          } else {
            improve(dp[pos + 1][o][e][a[pos] % 2],
                    dp[pos][o][e][last] + (last != (a[pos] % 2)));
          }
        }
      }
  }
  cout << min(dp[n][0][0][0], dp[n][0][0][1]) << endl;
}
