#include <bits/stdc++.h>
using namespace std;
long long dx[] = {1, 0, -1, 0};
long long dy[] = {0, 1, 0, -1};
long long gcd(long long x, long long y) {
  if (y == 0)
    return x;
  else
    return gcd(y, x % y);
}
long long expo(long long n, long long m, long long p) {
  long long r = 1;
  n = n % p;
  while (m > 0) {
    if (m % 2) r = (r * n) % p;
    n = (n * n) % p;
    m = m / 2;
  }
  return r % p;
}
bool isPrime(long long n) {
  if (n <= 1) return false;
  if (n <= 3) return true;
  if (n % 2 == 0 || n % 3 == 0) return false;
  for (long long i = 5; i * i <= n; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0) return false;
  return true;
}
long long n, p[105] = {0}, order[105], dp[105][105][105][3];
long long solve(long long i, long long odd, long long even, long long prev) {
  if (i == n + 1) return 0;
  if (dp[i][odd][even][prev] != -1) return dp[i][odd][even][prev];
  if (order[i] != 0) {
    dp[i][odd][even][prev] = ((i != 1 && prev % 2 != order[i] % 2) ? 1 : 0) +
                             solve(i + 1, odd, even, order[i] % 2);
    return dp[i][odd][even][prev];
  }
  long long ans = (1LL << 25);
  if (odd) {
    if (i != 1) {
      if (prev % 2 == 0)
        ans = 1;
      else
        ans = 0;
    } else
      ans = 0;
    ans = ans + solve(i + 1, odd - 1, even, 1);
  }
  if (even) {
    long long t = 0;
    if (i != 1) {
      if (prev % 2 == 1)
        t = 1;
      else
        t = 0;
    }
    t = t + solve(i + 1, odd, even - 1, 0);
    ans = min(ans, t);
  }
  dp[i][odd][even][prev] = ans;
  return ans;
}
int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  cin >> n;
  for (long long i = 1; i <= n; i++) {
    cin >> order[i];
    p[order[i]]++;
  }
  for (long long i = 0; i < 105; i++) {
    for (long long j = 0; j < 105; j++) {
      for (long long k = 0; k < 105; k++) {
        dp[i][j][k][0] = dp[i][j][k][1] = -1;
      }
    }
  }
  long long odd = 0, even = 0;
  for (long long i = 1; i <= n; i++) {
    if (p[i] == 0) {
      if (i % 2)
        odd++;
      else
        even++;
    }
  }
  cout << solve(1, odd, even, 0) << '\n';
}
