#include <bits/stdc++.h>
#pragma GCC optimize("O3")
using namespace std;
int n, dp[102][102][2], p[102], nr;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  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] = 1e9;
  dp[0][0][0] = dp[0][0][1] = 0;
  for (int i = 1; i <= n; i++) {
    nr += p[i] % 2;
    if (p[i] != 0) {
      for (int j = nr; j <= min(i, (n + 1) / 2); j++)
        if (p[i] % 2)
          dp[i][j][1] = min(dp[i - 1][j - 1][1], dp[i - 1][j - 1][0] + 1);
        else
          dp[i][j][0] = min(dp[i - 1][j][1] + 1, dp[i - 1][j][0]);
    } else {
      for (int j = nr + 1; j <= min(i, (n + 1) / 2); j++)
        dp[i][j][1] = min(dp[i - 1][j - 1][0] + 1, dp[i - 1][j - 1][1]);
      for (int j = nr; j <= min(i - 1, (n + 1) / 2); j++)
        dp[i][j][0] = min(dp[i - 1][j][0], dp[i - 1][j][1] + 1);
    }
  }
  cout << min(dp[n][(n + 1) / 2][0], dp[n][(n + 1) / 2][1]);
  return 0;
}
