#include <bits/stdc++.h>
using namespace std;
void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(char x) { cerr << '\'' << x << '\''; }
void __print(const char *x) { cerr << '\"' << x << '\"'; }
void __print(const string &x) { cerr << '\"' << x << '\"'; }
void __print(bool x) { cerr << (x ? "true" : "false"); }
template <typename T, typename V>
void __print(const pair<T, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename T>
void __print(const T &x) {
  int f = 0;
  cerr << '{';
  for (auto &i : x) cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\n"; }
template <typename T, typename... V>
void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v)) cerr << ", ";
  _print(v...);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int t = 1;
  while (t--) {
    long long int n = 0, m = 0, k = 0, i = 0, j = 0, p = 0, q = 0, x = 0, y = 0,
                  z = 0, ans = 0, cnt = 0, l = 0, r = 0, mid = 0, lo = 0,
                  hi = 0;
    string s;
    bool flag = false;
    cin >> n;
    long long int a[n + 1];
    for (i = 1; i <= n; i++) cin >> a[i];
    long long int dp[n + 1][n + 1][2];
    long long int even = n / 2;
    long long int odd = (n % 2 == 0) ? n / 2 : (n / 2) + 1;
    for (i = 0; i <= n; i++)
      for (j = 0; j <= n; j++)
        for (k = 0; k < 2; k++) dp[i][j][k] = 1000000007;
    dp[0][0][0] = 0;
    dp[0][0][1] = 0;
    for (i = 1; i <= n; i++)
      if (a[i] == 0)
        for (j = 0; j <= even; j++)
          if (j > i || (i - j) > odd)
            continue;
          else
            dp[i][j][0] = min(dp[i][j][0], dp[i - 1][j - 1][0]),
            dp[i][j][0] = min(dp[i][j][0], dp[i - 1][j - 1][1] + 1),
            dp[i][j][1] = min(dp[i][j][1], dp[i - 1][j][1]),
            dp[i][j][1] = min(dp[i][j][1], dp[i - 1][j][0] + 1);
      else
        for (j = 0; j <= even; j++) {
          if (j > i || (i - j) > odd) continue;
          if (a[i] % 2 == 0)
            dp[i][j][0] = min(dp[i][j][0], dp[i - 1][j - 1][0]),
            dp[i][j][0] = min(dp[i][j][0], dp[i - 1][j - 1][1] + 1);
          else
            dp[i][j][1] = min(dp[i][j][1], dp[i - 1][j][1]),
            dp[i][j][1] = min(dp[i][j][1], dp[i - 1][j][0] + 1);
        }
    ans = 1000000007;
    for (j = 0; j <= even; j++)
      ans = min(ans, dp[n][j][0]), ans = min(ans, dp[n][j][1]);
    cout << ans << endl;
    ;
  }
  return 0;
}
