#include <bits/stdc++.h>
using namespace std;
const int inf = 0x3f3f3f3f;
const int N = 110;
int a[N];
int dp[N][N][2];
int main() {
  std::ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> a[i];
  memset(dp, inf, sizeof dp);
  dp[0][0][0] = dp[0][0][1] = 0;
  for (int i = 1; i <= n; i++)
    for (int j = 0; j <= i; j++) {
      if (a[i] & 1 || a[i] == 0)
        dp[i][j][1] = min(dp[i - 1][j][1], dp[i - 1][j][0] + 1);
      if (a[i] % 2 == 0)
        dp[i][j][0] = min(dp[i - 1][j - 1][0], dp[i - 1][j - 1][1] + 1);
    }
  cout << min(dp[n][n / 2][0], dp[n][n / 2][1]) << '\n';
  return 0;
}
