#include <bits/stdc++.h>
using namespace std;
const int N = 103;
long long n, dp[N][N][2], a[N], z;
int main() {
  cin >> n;
  for (long long i = 1; i < n + 1; i++) cin >> a[i];
  for (long long i = 0; i < N; i++) {
    for (long long j = 0; j < N; j++) dp[i][j][0] = dp[i][j][1] = 1e9;
  }
  dp[0][0][0] = 0;
  dp[0][0][1] = 0;
  for (long long i = 1; i < n + 1; i++) {
    for (long long j = 0; j < i + 1; j++) {
      if (a[i] % 2 == 0)
        dp[i][j][0] = min(dp[i - 1][j - 1][0], dp[i - 1][j - 1][1] + 1);
      if (a[i] % 2 == 1 || a[i] == 0)
        dp[i][j][1] = min(dp[i - 1][j][0] + 1, dp[i - 1][j][1]);
    }
  }
  cout << min(dp[n][n / 2][0], dp[n][n / 2][1]);
}
