#include <bits/stdc++.h>
using namespace std;
const long long N = 100 + 5;
const int inf = 0x3f3f3f3f;
long long n;
long long arr[N];
long long dp[N][N][N][2];
void solve() {
  cin >> n;
  int num0, num1;
  if (n % 2) {
    num0 = n / 2;
    num1 = n / 2 + 1;
  } else {
    num0 = n / 2;
    num1 = n / 2;
  }
  for (long long i = 1; i <= n; i++) {
    cin >> arr[i];
  }
  memset(dp, inf, sizeof dp);
  dp[0][0][0][0] = 0;
  dp[0][0][0][1] = 0;
  for (long long i = 1; i <= n; i++) {
    for (long long j = 0; j <= num1; j++) {
      for (long long k = 0; k <= num0; k++) {
        if (arr[i]) {
          if (arr[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][0], dp[i - 1][j][k - 1][1] + 1);
          }
        } else {
          if (j > 0)
            dp[i][j][k][1] =
                min(dp[i - 1][j - 1][k][0] + 1, dp[i - 1][j - 1][k][1]);
          if (k > 0)
            dp[i][j][k][0] =
                min(dp[i - 1][j][k - 1][0], dp[i - 1][j][k - 1][1] + 1);
        }
      }
    }
  }
  cout << min(dp[n][num1][num0][1], dp[n][num1][num0][0]);
}
int main() {
  long long T = 1;
  ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL);
  while (T--) solve();
  return 0;
}
