#include <bits/stdc++.h>
using namespace std;
const int maxn = 100 + 10;
inline int read() {
  char c = getchar();
  int x = 0, f = 1;
  while (c < '0' || c > '9') {
    if (c == '-') f = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    x = x * 10 + c - '0';
    c = getchar();
  }
  return x * f;
}
int cnt1, cnt2;
int num[maxn];
int dp[maxn][maxn][maxn][2];
int main() {
  int n;
  cin >> n;
  cnt2 = n / 2;
  cnt1 = n - cnt2;
  for (int i = 1; i <= n; ++i) {
    num[i] = read();
  }
  memset(dp, 0x3f, sizeof(dp));
  dp[0][0][0][0] = dp[0][0][0][1] = 0;
  for (int i = 1; i <= n; ++i) {
    if (num[i]) {
      if (num[i] & 1) {
        for (int j = 1; j <= i; ++j) {
          dp[i][j][i - j][1] =
              min(dp[i - 1][j - 1][i - j][1], dp[i - 1][j - 1][i - j][0] + 1);
        }
      } else {
        for (int j = 0; j < i; ++j) {
          dp[i][j][i - j][0] =
              min(dp[i - 1][j][i - j - 1][0], dp[i - 1][j][i - j - 1][1] + 1);
        }
      }
    } else {
      for (int j = 1; j <= i; ++j) {
        dp[i][j][i - j][1] =
            min(dp[i - 1][j - 1][i - j][1], dp[i - 1][j - 1][i - j][0] + 1);
      }
      for (int j = 0; j < i; ++j) {
        dp[i][j][i - j][0] =
            min(dp[i - 1][j][i - j - 1][0], dp[i - 1][j][i - j - 1][1] + 1);
      }
    }
  }
  printf("%d\n", min(dp[n][cnt1][cnt2][0], dp[n][cnt1][cnt2][1]));
  return 0;
}
