#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
const int N = 2e5 + 5;
int a[105];
int dp[105][105][2];
int main() {
  int n;
  cin >> n;
  int cnt0 = 0, cnt1 = 0;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    if (a[i]) {
      if (a[i] % 2)
        cnt1++;
      else
        cnt0++;
    }
  }
  memset(dp, 0x3f, sizeof dp);
  cnt0 = n / 2 - cnt0, cnt1 = (n + 1) / 2 - cnt1;
  if (a[1] == 0) {
    dp[1][0][0] = dp[1][1][1] = 0;
  } else if (a[1] % 2) {
    dp[1][0][1] = 0;
  } else
    dp[1][0][0] = 0;
  for (int i = 2; i <= n; i++) {
    if (a[i] % 2) {
      for (int j = 0; j <= cnt1; j++) {
        dp[i][j][1] = min(dp[i - 1][j][1], dp[i - 1][j][0] + 1);
      }
    } else if (a[i]) {
      for (int j = 0; j <= cnt1; j++) {
        dp[i][j][0] = min(dp[i - 1][j][1] + 1, dp[i - 1][j][0]);
      }
    } else {
      for (int j = 0; j <= cnt1; j++) {
        if (j == 0)
          dp[i][j][0] = min(dp[i - 1][j][1] + 1, dp[i - 1][j][0]);
        else {
          dp[i][j][1] = min(dp[i - 1][j - 1][1], dp[i - 1][j - 1][0] + 1);
          dp[i][j][0] = min(dp[i - 1][j][1] + 1, dp[i - 1][j][0]);
        }
      }
    }
  }
  cout << min(dp[n][cnt1][0], dp[n][cnt1][1]) << endl;
  return 0;
}
