#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long n;
  cin >> n;
  long long a[n + 1];
  for (long long i = 0; i < n; i++) {
    long long x;
    cin >> x;
    if (x == 0)
      a[i + 1] = -1;
    else
      a[i + 1] = x % 2;
  }
  long long dp[n + 1][n + 1][2];
  for (long long i = 0; i < n + 1; i++) {
    for (long long j = 0; j < n + 1; j++) {
      dp[i][j][0] = INT_MAX;
      dp[i][j][1] = INT_MAX;
    }
  }
  if (a[1] == -1) {
    dp[1][0][1] = 0;
    dp[1][1][0] = 0;
  } else if (a[1] == 0) {
    dp[1][1][0] = 0;
  } else
    dp[1][0][1] = 0;
  for (long long i = 2; i <= n; i++) {
    for (long long j = 0; j <= i; j++) {
      if (a[i] == -1) {
        if (j == 0) {
          dp[i][j][1] = min(dp[i - 1][j][1], dp[i - 1][j][0] + 1);
          continue;
        }
        dp[i][j][0] = min(dp[i - 1][j - 1][1] + 1, dp[i - 1][j - 1][0]);
        dp[i][j][1] = min(dp[i - 1][j][1], dp[i - 1][j][0] + 1);
      } else if (a[i] == 0) {
        if (j == 0) {
          continue;
        }
        dp[i][j][0] = min(dp[i - 1][j - 1][1] + 1, dp[i - 1][j - 1][0]);
      } else {
        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;
}
