#include <bits/stdc++.h>
using namespace std;
const int N = 205;
int n;
int p[N];
int f[N][2][N];
int main() {
  memset(f, 0x3f, sizeof(f));
  cin.sync_with_stdio(false);
  cin >> n;
  int even = n / 2 + (n & 1);
  for (int i = 1; i <= n; i++) {
    cin >> p[i];
    p[i] = p[i] ? (p[i] & 1) : -1;
  }
  f[0][0][0] = f[0][1][0] = 0;
  for (int i = 1; i <= n; i++)
    for (int j = 0; j < 2; j++) {
      if (p[i] >= 0 && p[i] != j) {
        continue;
      }
      for (int k = 0; k <= min(i, even); k++) {
        if (j == 1) {
          if (k) {
            f[i][1][k] = min(f[i - 1][1][k - 1], f[i - 1][0][k - 1] + 1);
          }
        } else {
          f[i][0][k] = min(f[i - 1][0][k], f[i - 1][1][k] + 1);
        }
      }
    }
  cout << min(f[n][0][even], f[n][1][even]) << endl;
}
