#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-8;
const double pi = acos(-1.0);
const long long INF = 0x3f3f3f3f3f3f3f3f;
const int inf = 0x3f3f3f3f;
const int N = 100 + 5;
int n;
int a[N];
long long dp[N][N][N][2];
void INIT() { memset(dp, 0x3f, sizeof(dp)); }
void solve() {
  INIT();
  int num0, num1;
  if (n % 2) {
    num0 = n / 2;
    num1 = n / 2 + 1;
  } else {
    num0 = n / 2;
    num1 = n / 2;
  }
  for (int i = 1; i <= n; i++) {
    cin >> (a[i]);
  }
  dp[0][0][0][0] = dp[0][0][0][1] = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j <= num1; j++) {
      for (int k = 0; k <= num0; k++) {
        if (a[i] == 0) {
          if (k > 0)
            dp[i][j][k][0] =
                min(dp[i - 1][j][k - 1][0], dp[i - 1][j][k - 1][1] + 1);
          if (j > 0)
            dp[i][j][k][1] =
                min(dp[i - 1][j - 1][k][0] + 1, dp[i - 1][j - 1][k][1]);
        } else {
          if (a[i] % 2) {
            if (j > 0)
              dp[i][j][k][1] =
                  min(dp[i - 1][j - 1][k][0] + 1, dp[i - 1][j - 1][k][1]);
          } else {
            if (k > 0)
              dp[i][j][k][0] =
                  min(dp[i - 1][j][k - 1][1] + 1, dp[i - 1][j][k - 1][0]);
          }
        }
      }
    }
  }
  cout << (min(dp[n][num1][num0][0], dp[n][num1][num0][1])) << '\n';
}
int main() {
  ios::sync_with_stdio(false);
  while (cin >> n) {
    solve();
  }
  return 0;
}
