#include <bits/stdc++.h>
using namespace std;
const long long MOD = 10000000007;
const int maxn = 100010;
const int MAX = 10010;
const long long linf = 0x3f3f3f3f3f3f3f3f;
const int inf = 0x3f3f3f3f;
long long qpow(long long a, long long b) {
  return b ? ((b & 1) ? a * qpow(a * a % MOD, b >> 1) % MOD
                      : qpow(a * a % MOD, b >> 1)) %
                 MOD
           : 1;
}
long long qpow(long long a, long long b, long long c) {
  return b ? ((b & 1) ? a * qpow(a * a % MOD, b >> 1) % c
                      : qpow(a * a % MOD, b >> 1)) %
                 c
           : 1;
}
inline int ird() {
  register int x = 0, f = 1;
  register char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9')
    x = (x << 3) + (x << 1) + ch - '0', ch = getchar();
  return x * f;
}
inline long long lrd() {
  register long long x = 0, f = 1;
  register char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9')
    x = (x << 3) + (x << 1) + ch - '0', ch = getchar();
  return x * f;
}
long long gcd(long long a, long long b) { return (b > 0) ? gcd(b, a % b) : a; }
int dp[110][110][2];
int a[110], sum[110];
int main() {
  for (int i = 0; i <= 110; i++) {
    for (int j = 0; j <= 110; j++) {
      dp[i][j][0] = MAX;
      dp[i][j][1] = MAX;
    }
  }
  memset(sum, 0, sizeof sum);
  int n, ji = 0, ou = 0;
  n = ird();
  ou = n / 2;
  ji = n - ou;
  for (int i = 1; i <= n; i++) {
    a[i] = ird();
    sum[i] = sum[i - 1];
    if (a[i] % 2 == 1) sum[i]++;
  }
  if (a[1] != 0) {
    if (a[1] % 2 == 0) {
      dp[1][0][0] = 0;
    } else {
      dp[1][1][1] = 0;
    }
  } else {
    dp[1][1][1] = 0;
    dp[1][0][0] = 0;
  }
  for (int i = 2; i <= n; i++) {
    if (a[i] != 0) {
      if (a[i] % 2 == 0) {
        for (int j = max(sum[i], i - ji); j <= min(i, ji); j++) {
          dp[i][j][0] = min(dp[i - 1][j][1] + 1, dp[i - 1][j][0]);
        }
      } else {
        if (a[i] % 2 == 1) {
          for (int j = max(sum[i], i - ji); j <= min(ji, i); j++) {
            dp[i][j][1] = min(dp[i - 1][j - 1][0] + 1, dp[i - 1][j - 1][1]);
          }
        }
      }
    } else {
      for (int j = max(sum[i], i - ji); j <= min(i, ji); j++) {
        dp[i][j][0] = min(dp[i - 1][j][0], dp[i - 1][j][1] + 1);
      }
      for (int j = max(sum[i], i - ji); j <= min(i, ji); j++)
        dp[i][j][1] = min(dp[i - 1][j - 1][0] + 1, dp[i - 1][j - 1][1]);
    }
  }
  cout << min(dp[n][ji][1], dp[n][ji][0]) << endl;
  return 0;
}
