#include <bits/stdc++.h>
using namespace std;
const int maxn = 110;
int n, a[maxn], dp[maxn][maxn][2];
int main() {
  ios_base::sync_with_stdio(0);
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
  }
  memset(dp, 0x3f, sizeof(dp));
  if (n > 1 && (a[1] == 0 || a[1] % 2 == 0)) dp[1][n / 2 - 1][0] = 0;
  if (a[1] % 2 == 1 || a[1] == 0) dp[1][n / 2][1] = 0;
  for (int i = 2; i <= n; i++) {
    for (int j = 0; j <= n / 2; j++) {
      for (int k = 0; k < 2; k++) {
        if (j > 0 && (a[i] == 0 || a[i] % 2 == 0))
          dp[i][j - 1][0] = min(dp[i][j - 1][0], dp[i - 1][j][k] + (k == 1));
        if (i + j - 1 < n && (a[i] == 0 || a[i] % 2 == 1))
          dp[i][j][1] = min(dp[i][j][1], dp[i - 1][j][k] + (k == 0));
      }
    }
  }
  cout << min(dp[n][0][0], dp[n][0][1]) << endl;
  return 0;
}
