#include <bits/stdc++.h>
using namespace std;
int p[101], dp[101][101][2];
int main() {
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> p[i];
  }
  for (int i = 0; i <= n; i++) {
    for (int j = 0; j <= n; j++) {
      dp[i][j][0] = dp[i][j][1] = 9999999;
    }
  }
  dp[0][0][0] = dp[0][0][1] = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j <= i; j++) {
      if (p[i] % 2 == 0) {
        if (j > 0)
          dp[i][j][0] = min(dp[i - 1][j - 1][0], dp[i - 1][j - 1][1] + 1);
      }
      if (p[i] % 2 == 1 || p[i] == 0) {
        dp[i][j][1] = min(dp[i - 1][j][1], dp[i - 1][j][0] + 1);
      }
    }
  }
  cout << min(dp[n][n / 2][0], dp[n][n / 2][1]) << endl;
  return 0;
}
