#include <bits/stdc++.h>
using namespace std;
long long int fastMax(long long int x, long long int y) {
  return (((y - x) >> (32 - 1)) & (x ^ y)) ^ y;
}
long long int fastMin(long long int x, long long int y) {
  return (((y - x) >> (32 - 1)) & (x ^ y)) ^ x;
}
const long long int MAXN = 103;
long long int a[MAXN];
long long int even = 0, odd = 0;
long long int dp[MAXN][MAXN][MAXN][2];
long long int n;
long long int rec(long long int idx, long long int el, long long int ol,
                  long long int prev) {
  if (idx == n + 1) return 0;
  long long int &ans = dp[idx][el][ol][prev];
  if (ans != -1) return ans;
  if (a[idx] != 0) {
    if (prev == a[idx] % 2)
      return ans = rec(idx + 1, el, ol, a[idx] % 2);
    else
      return ans = rec(idx + 1, el, ol, a[idx] % 2) + 1;
  }
  ans = 1000;
  if (ol > 0) {
    if (prev == 1)
      ans = min(ans, rec(idx + 1, el, ol - 1, 1));
    else
      ans = min(ans, rec(idx + 1, el, ol - 1, 1) + 1);
  }
  if (el > 0) {
    if (prev == 1)
      ans = min(ans, rec(idx + 1, el - 1, ol, 0) + 1);
    else
      ans = min(ans, rec(idx + 1, el - 1, ol, 0));
  }
  return ans;
}
void solve() {
  cin >> n;
  for (long long int i = 1; i <= n; i++) {
    cin >> a[i];
    if (i & 1)
      odd++;
    else
      even++;
    if (a[i] == 0) continue;
    if (a[i] & 1)
      odd--;
    else
      even--;
  }
  memset((dp), -1, sizeof((dp)));
  cout << min(rec(1, even, odd, 0), rec(1, even, odd, 1)) << '\n';
}
signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  long long int t = 1;
  for (long long int i = (1); i <= (t); ++i) {
    solve();
  }
}
