#include <bits/stdc++.h>
using namespace std;
int dp[200][200][2];
int p[200];
int n;
vector<int> em;
int even, odd;
int calc(int i, int j) {
  int res = 0;
  if (p[i - 1]) res += ((p[i - 1] % 2) != (j));
  if (p[i + 1]) res += ((p[i + 1] % 2) != (j));
  return res;
}
int calc2(int i, int j) {
  int res = 0;
  if (p[i - 1]) res += ((p[i - 1] % 2) != (j));
  return res;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cin >> n;
  even = n / 2;
  odd = (n + 1) / 2;
  for (int i = 1; i <= n; i++) {
    cin >> p[i];
    if (p[i] == 0)
      em.push_back(i);
    else {
      if (p[i] % 2 == 0)
        even--;
      else
        odd--;
    }
  }
  int x = 0;
  for (int i = 1; i <= n; i++) {
    if (p[i] != 0) x += calc2(i, p[i] % 2);
  }
  if (!em.size()) {
    cout << x << endl;
    return 0;
  }
  memset(dp, 63, sizeof(dp));
  dp[0][1][0] = calc(em[0], 0);
  dp[0][0][1] = calc(em[0], 1);
  for (int i = 1; i < em.size(); i++) {
    for (int ce = 0; ce <= i + 1; ce++) {
      int co = i + 1 - ce;
      if (em[i - 1] == em[i] - 1) {
        if (!ce) goto e1;
        dp[i][ce][0] = min(dp[i - 1][ce - 1][0], dp[i - 1][ce - 1][1] + 1) +
                       calc(em[i], 0);
      e1:;
        if (!co) goto e2;
        dp[i][ce][1] =
            min(dp[i - 1][ce][0] + 1, dp[i - 1][ce][1]) + calc(em[i], 1);
      e2:;
      } else {
        if (!ce) goto e3;
        dp[i][ce][0] =
            min(dp[i - 1][ce - 1][0], dp[i - 1][ce - 1][1]) + calc(em[i], 0);
      e3:;
        if (!co) goto e4;
        dp[i][ce][1] = min(dp[i - 1][ce][0], dp[i - 1][ce][1]) + calc(em[i], 1);
      e4:;
      }
    }
  }
  cout << min(dp[em.size() - 1][even][0], dp[em.size() - 1][even][1]) + x
       << endl;
  return 0;
}
