#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target("sse4")
using namespace std;
using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using str = string;
const char nl = '\n';
;
str to_string(char c) { return str(1, c); }
str to_string(bool b) { return b ? "true" : "false"; }
str to_string(const char* second) { return (str)second; }
str to_string(str second) { return second; }
template <class A>
str to_string(complex<A> c) {
  stringstream ss;
  ss << c;
  return ss.str();
}
str to_string(vector<bool> v) {
  str res = "{";
  for (int i = 0; i < v.size(); i++) res += char('0' + v[i]);
  res += "}";
  return res;
}
template <size_t SZ>
str to_string(bitset<SZ> b) {
  str res = "";
  for (int i = 0; i < b.size(); i++) res += char('0' + b[i]);
  return res;
}
template <class A, class B>
str to_string(pair<A, B> p);
template <class T>
str to_string(T v) {
  bool fst = 1;
  str res = "{";
  for (const auto& x : v) {
    if (!fst) res += ", ";
    fst = 0;
    res += to_string(x);
  }
  res += "}";
  return res;
}
template <class A, class B>
str to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
void DBG() { cerr << "]" << endl; }
template <class H, class... T>
void DBG(H h, T... t) {
  cerr << to_string(h);
  if (sizeof...(t)) cerr << ", ";
  DBG(t...);
}
const int N = 205;
int dp[N][N][2];
signed main() {
  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
  memset(dp, 0x3f, sizeof(dp));
  int n;
  cin >> n;
  vi inp(n + 1);
  for (int i = 1; i < n + 1; i++) {
    cin >> inp[i];
  }
  dp[0][0][0] = dp[0][0][1] = 0;
  for (int i = 1; i <= n; i++) {
    for (int k = 0; k <= i; k++) {
      if (k && ((inp[i] & 1) || (!inp[i]))) {
        dp[i][k][1] =
            min(dp[i][k][1], min(dp[i - 1][k - 1][0] + 1, dp[i - 1][k - 1][1]));
      }
      if (!(inp[i] & 1) || !inp[i]) {
        dp[i][k][0] =
            min(dp[i][k][0], min(dp[i - 1][k][0], dp[i - 1][k][1] + 1));
      }
      0;
    }
  }
  cout << min(dp[n][(n + 1) / 2][0], dp[n][(n + 1) / 2][1]) << nl;
}
