#include <bits/stdc++.h>
using namespace std;
int n;
vector<int> a;
int dp[101][3][101][101];
int f(int i, int par, int ne, int no) {
  if (i == n) {
    return 0;
  }
  if (dp[i][par][ne][no] != -1) {
    return dp[i][par][ne][no];
  }
  if (a[i] != 0) {
    int val = 0;
    if (par != 2 && a[i] % 2 != par) {
      val += 1;
    }
    dp[i][par][ne][no] = val + f(i + 1, a[i] % 2, ne, no);
    return dp[i][par][ne][no];
  }
  int ans = INT_MAX;
  if (par == 0) {
    if (ne) {
      ans = min(ans, f(i + 1, 0, ne - 1, no));
    }
    if (no) {
      ans = min(ans, 1 + f(i + 1, 1, ne, no - 1));
    }
  } else if (par == 1) {
    if (ne) {
      ans = min(ans, 1 + f(i + 1, 0, ne - 1, no));
    }
    if (no) {
      ans = min(ans, f(i + 1, 1, ne, no - 1));
    }
  } else {
    if (ne) {
      ans = min(ans, f(i + 1, 0, ne - 1, no));
    }
    if (no) {
      ans = min(ans, f(i + 1, 1, ne, no - 1));
    }
  }
  dp[i][par][ne][no] = ans;
  return ans;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  cin >> n;
  a.resize(n);
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < 3; j++) {
      for (int k = 0; k < n; k++) {
        for (int l = 0; l < n; l++) {
          dp[i][j][k][l] = -1;
        }
      }
    }
  }
  int ne = n / 2;
  int no = n - ne;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] == 0) continue;
    if (a[i] % 2)
      no--;
    else
      ne--;
  }
  cout << f(0, 2, ne, no) << '\n';
  return 0;
}
