#include <bits/stdc++.h>
using namespace std;
const int N = 102;
int n;
int a[N];
int p[N];
int dp[N][N][N][2];
int f(int i, int odd, int even, int last) {
  if (odd < 0 or even < 0) return 1e9;
  if (i == n) return 0;
  int &ans = dp[i][odd][even][last];
  if (~ans) return ans;
  ans = 1e9;
  if (a[i]) {
    ans = f(i + 1, odd, even, a[i] % 2);
    if (i > 0 and a[i] % 2 != last) {
      ans++;
    }
  } else {
    int tmp = f(i + 1, odd - 1, even, 1);
    if (i > 0 and last != 1) tmp++;
    ans = min(ans, tmp);
    tmp = f(i + 1, odd, even - 1, 0);
    if (i > 0 and last != 0) tmp++;
    ans = min(ans, tmp);
  }
  return ans;
}
int main() {
  memset(dp, -1, sizeof dp);
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d", a + i);
  int odd = 0, even = 0;
  for (int i = 1; i <= n; i++) {
    (i % 2 ? odd : even)++;
  }
  for (int i = 0; i < n; i++) {
    if (a[i] > 0) {
      if (a[i] % 2 == 1)
        odd--;
      else
        even--;
    }
  }
  printf("%d\n", f(0, odd, even, 0));
}
