#include <bits/stdc++.h>
using namespace std;
int dp[105][105][2], a[105];
int n;
void printdp() {
  int cnt = 0;
  for (int i = 0; i < n + 1; i++) {
    for (int j = 0; j < n + 1; j++) {
      for (int k = 0; k < 2; k++) {
        cnt++;
        cout << "index  " << i << " " << j << " " << k << " " << dp[i][j][k]
             << " ";
      }
      cout << endl;
    }
    cout << endl;
  }
  cout << endl << cnt << endl;
}
int main() {
  cin >> n;
  for (int i = 0; i < n + 1; i++) {
    for (int j = 0; j < n + 1; j++) {
      for (int k = 0; k < 2; k++) {
        dp[i][j][k] = n + 1;
      }
    }
  }
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
  }
  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] % 2 || a[i] == 0) {
        dp[i][j][1] = min(dp[i - 1][j][0] + 1, dp[i - 1][j][1]);
      }
      if (a[i] % 2 == 0 && j > 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]) << endl;
}
