#include <bits/stdc++.h>
using namespace std;
void cline() { cout << '\n'; }
template <typename T, typename... V>
void cline(T t, V... v) {
  cout << t;
  if (sizeof...(v)) cout << ' ';
  cline(v...);
}
void cspc() { cout << ' '; }
template <typename T, typename... V>
void cspc(T t, V... v) {
  cout << t;
  if (sizeof...(v)) cout << ' ';
  cspc(v...);
}
int n;
int a[105];
int dp[104][52][52][2];
int calc(int indx, int even, int odd, int pre) {
  if (indx == n) return 0;
  if (dp[indx][even][odd][pre] != -1) return dp[indx][even][odd][pre];
  if (indx == 0) {
    if (a[indx] == 0) {
      if (even == 0) {
        return dp[indx][even][odd][pre] = calc(indx + 1, even, odd - 1, 1);
      } else if (odd == 0) {
        return dp[indx][even][odd][pre] = calc(indx + 1, even - 1, odd, 0);
      } else {
        return dp[indx][even][odd][pre] = min(calc(indx + 1, even, odd - 1, 1),
                                              calc(indx + 1, even - 1, odd, 0));
      }
    } else {
      return dp[indx][even][odd][pre] = calc(indx + 1, even, odd, a[indx] % 2);
    }
  } else {
    if (a[indx] == 0) {
      if (even == 0) {
        if (pre % 2 == 0) {
          return dp[indx][even][odd][pre] =
                     calc(indx + 1, even, odd - 1, 1) + 1;
        } else {
          return dp[indx][even][odd][pre] = calc(indx + 1, even, odd - 1, 1);
        }
      } else if (odd == 0) {
        if (pre % 2 == 1) {
          return dp[indx][even][odd][pre] =
                     calc(indx + 1, even - 1, odd, 0) + 1;
        } else {
          return dp[indx][even][odd][pre] = calc(indx + 1, even - 1, odd, 0);
        }
      } else {
        if (pre % 2 != 0) {
          return dp[indx][even][odd][pre] =
                     min(calc(indx + 1, even, odd - 1, 1),
                         calc(indx + 1, even - 1, odd, 0) + 1);
        } else {
          return dp[indx][even][odd][pre] =
                     min(calc(indx + 1, even, odd - 1, 1) + 1,
                         calc(indx + 1, even - 1, odd, 0));
        }
      }
    } else {
      if (a[indx] % 2 != pre % 2) {
        return dp[indx][even][odd][pre] =
                   calc(indx + 1, even, odd, a[indx] % 2) + 1;
      } else {
        return dp[indx][even][odd][pre] =
                   calc(indx + 1, even, odd, a[indx] % 2);
      }
    }
  }
}
int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  int even = n / 2, odd = (n + 1) / 2;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] % 2 == 0)
      even--;
    else
      odd--;
    if (a[i] == 0) even++;
  }
  for (int in1 = 0; in1 < 104; in1++) {
    for (int in2 = 0; in2 < 52; in2++) {
      for (int in3 = 0; in3 < 52; in3++) {
        dp[in1][in2][in3][0] = -1;
        dp[in1][in2][in3][1] = -1;
      }
    }
  }
  cspc(calc(0, even, odd, 0));
  return 0;
}
