#include <bits/stdc++.h>
using namespace std;
long long int arr[100001], done[100001], cnt0[100001], cnte[100001],
    cnto[100001];
long long int dp[105][105][2];
int main() {
  ios::sync_with_stdio(false);
  ;
  cin.tie(0);
  ;
  long long int i, j, n, k, l, x, y, evenLeft = 0, oddLeft = 0, z;
  cin >> n;
  for (i = 1; i <= n; i++) {
    cin >> arr[i];
    if (arr[i] != 0) done[arr[i]] = 1;
  }
  oddLeft = 0;
  evenLeft = 0;
  for (i = 1; i <= n; i++) {
    if (done[i]) continue;
    if (i & 1)
      oddLeft++;
    else
      evenLeft++;
  }
  for (i = 1; i <= n; i++) cnt0[i] = cnt0[i - 1] + (arr[i] == 0);
  for (i = 1; i <= n; i++) {
    cnte[i] = cnte[i - 1];
    if (arr[i] != 0 && arr[i] % 2 == 0) cnte[i]++;
  }
  for (i = 1; i <= n; i++) {
    cnto[i] = cnto[i - 1];
    if (arr[i] != 0 && arr[i] & 1) cnto[i]++;
  }
  for (i = 0; i <= n; i++) {
    for (j = 0; j <= n; j++) {
      for (k = 0; k <= 1; k++) dp[i][j][k] = 1000000000000;
    }
  }
  if (arr[1] != 0) {
    if (arr[1] & 1)
      dp[1][evenLeft][1] = 0;
    else
      dp[1][evenLeft][0] = 0;
  } else {
    if (evenLeft > 0) dp[1][evenLeft - 1][0] = 0;
    if (oddLeft > 0) dp[1][evenLeft][1] = 0;
  }
  for (i = 1; i < n; i++) {
    for (j = 0; j <= evenLeft; j++) {
      for (k = 0; k <= 1; k++) {
        if (dp[i][j][k] == 1000000000000) continue;
        x = cnt0[i];
        y = evenLeft - j;
        z = oddLeft - (x - y);
        if (arr[i + 1] != 0) {
          if (arr[i + 1] % 2 == k)
            dp[i + 1][j][arr[i + 1] % 2] =
                min(dp[i + 1][j][arr[i + 1] % 2], dp[i][j][k]);
          else
            dp[i + 1][j][arr[i + 1] % 2] =
                min(dp[i + 1][j][arr[i + 1] % 2], dp[i][j][k] + 1);
        } else {
          if (j > 0) {
            if (k == 0)
              dp[i + 1][j - 1][0] = min(dp[i + 1][j - 1][0], dp[i][j][k]);
            else
              dp[i + 1][j - 1][0] = min(dp[i + 1][j - 1][0], dp[i][j][k] + 1);
          }
          if (z > 0) {
            if (k == 0)
              dp[i + 1][j][1] = min(dp[i + 1][j][1], dp[i][j][k] + 1);
            else
              dp[i + 1][j][1] = min(dp[i + 1][j][1], dp[i][j][k]);
          }
        }
      }
    }
  }
  cout << min(dp[n][0][0], dp[n][0][1]);
  return 0;
}
