#include <bits/stdc++.h>
using namespace std;
int p[101], dp[101][101][2];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
  int n;
  cin >> n;
  for (int i = 0; i < n; ++i) {
    cin >> p[i];
    if (p[i] == 0)
      p[i] = -1;
    else
      p[i] %= 2;
  }
  for (int i = 0; i <= n / 2; ++i) {
    for (int j = 0; j <= (n + 1) / 2; ++j) dp[i][j][0] = dp[i][j][1] = 1e9;
  }
  dp[0][0][0] = dp[0][0][1] = 0;
  for (int i = 0; i <= n / 2; ++i) {
    for (int j = 0; j <= (n + 1) / 2; ++j) {
      int idx = i + j;
      if (dp[i][j][0] != 1e9) {
        if (p[idx] != 1) dp[i + 1][j][0] = min(dp[i][j][0], dp[i + 1][j][0]);
        if (p[idx] != 0)
          dp[i][j + 1][1] = min(1 + dp[i][j][0], dp[i][j + 1][1]);
      }
      if (dp[i][j][1] != 1e9) {
        if (p[idx] != 1)
          dp[i + 1][j][0] = min(1 + dp[i][j][1], dp[i + 1][j][0]);
        if (p[idx] != 0) dp[i][j + 1][1] = min(dp[i][j][1], dp[i][j + 1][1]);
      }
    }
  }
  cout << min(dp[n / 2][(n + 1) / 2][0], dp[n / 2][(n + 1) / 2][1]) << '\n';
}
