#include <bits/stdc++.h>
using namespace std;
void mahakal() {}
long long dx[4] = {1, 0, -1, 0};
long long dy[4] = {0, 1, 0, -1};
char c[4] = {'D', 'R', 'U', 'L'};
const long long maxN = 2e5 + 5;
long long n, a[110], dp[110][110][110][2];
void init() {
  for (long long i = 0; i < 110; i++) {
    for (long long j = 0; j < 110; j++) {
      for (long long k = 0; k < 110; k++) {
        dp[i][j][k][0] = 100000000000000000;
        dp[i][j][k][1] = 100000000000000000;
      }
    }
  }
  dp[0][0][0][0] = dp[0][0][0][1] = 0;
}
void solve() {
  cin >> n;
  for (long long i = 1; i <= n; i++) cin >> a[i];
  init();
  long long e = n / 2, o = n - e;
  for (long long i = 1; i <= n; i++) {
    for (long long j = 0; j <= o; j++) {
      for (long long k = 0; k <= e; k++) {
        if (a[i] == 0) {
          if (k > 0)
            dp[i][j][k][0] =
                min(dp[i - 1][j][k - 1][0], dp[i - 1][j][k - 1][1] + 1);
          if (j > 0)
            dp[i][j][k][1] =
                min(dp[i - 1][j - 1][k][1], dp[i - 1][j - 1][k][0] + 1);
        } else {
          if (a[i] % 2) {
            if (j > 0)
              dp[i][j][k][1] =
                  min(dp[i - 1][j - 1][k][1], dp[i - 1][j - 1][k][0] + 1);
          } else {
            if (k > 0)
              dp[i][j][k][0] =
                  min(dp[i - 1][j][k - 1][0], dp[i - 1][j][k - 1][1] + 1);
          }
        }
      }
    }
  }
  cout << min(dp[n][o][e][1], dp[n][o][e][0]) << endl;
}
int main() {
  mahakal();
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  long long t = 1;
  while (t--) solve();
  cerr << "\ntime taken : " << (float)clock() / CLOCKS_PER_SEC << " secs"
       << endl;
  return 0;
}
