#include <bits/stdc++.h>
using namespace std;
const int maxn = 105;
int dp[maxn][maxn][maxn][2];
int a[maxn];
int main() {
  int n;
  scanf("%d", &n);
  int cnt0, cnt1;
  cnt0 = cnt1 = 0;
  int zero = 0;
  for (int i = 1; i <= n; ++i) {
    scanf("%d", &a[i]);
    if (a[i] == 0) zero++;
    cnt1 += a[i] & 1;
  }
  cnt1 = (n + 1) / 2 - cnt1;
  cnt0 = zero - cnt1;
  memset(dp, 0x3f, sizeof(dp));
  if (cnt0 == 0) {
    for (int i = 1; i <= n; ++i) {
      if (a[i] == 0) {
        a[i] = 1;
      }
    }
    int ans = 0;
    for (int i = 2; i <= n; ++i) {
      int t1 = a[i] % 2;
      int t2 = a[i - 1] % 2;
      if (t1 != t2) ans++;
    }
    cout << ans << endl;
    return 0;
  }
  if (cnt1 == 0) {
    int ans = 0;
    for (int i = 2; i <= n; ++i) {
      int t1 = a[i] % 2;
      int t2 = a[i - 1] % 2;
      if (t1 != t2) ans++;
    }
    cout << ans << endl;
    return 0;
  }
  if (a[1] == 0) {
    dp[1][cnt0][cnt1 - 1][1] = 0;
    dp[1][cnt0 - 1][cnt1][0] = 0;
  } else {
    if (a[1] & 1) {
      dp[1][cnt0][cnt1][1] = 0;
    } else
      dp[1][cnt0][cnt1][0] = 0;
  }
  for (int i = 2; i <= n; ++i) {
    if (a[i] != 0) {
      if (a[i] & 1) {
        for (int j = 0; j <= cnt0; ++j) {
          for (int k = 0; k <= cnt1; ++k) {
            dp[i][j][k][1] = min(dp[i - 1][j][k][1], dp[i - 1][j][k][0] + 1);
          }
        }
      } else {
        for (int j = 0; j <= cnt0; ++j) {
          for (int k = 0; k <= cnt1; ++k) {
            dp[i][j][k][0] = min(dp[i - 1][j][k][1] + 1, dp[i - 1][j][k][0]);
          }
        }
      }
      continue;
    }
    for (int j = 0; j <= cnt0; ++j) {
      for (int k = 0; k <= cnt1; ++k) {
        dp[i][j][k][0] =
            min(dp[i - 1][j + 1][k][0], dp[i - 1][j + 1][k][1] + 1);
        dp[i][j][k][1] =
            min(dp[i - 1][j][k + 1][0] + 1, dp[i - 1][j][k + 1][1]);
      }
    }
  }
  cout << min(dp[n][0][0][0], dp[n][0][0][1]) << endl;
  return 0;
}
