#include <bits/stdc++.h>
const int INF = 0x3f3f3f3f;
using namespace std;
int a[105], n, dp[105][105][2], cnt = 0;
int main() {
  scanf("%d", &n);
  cnt = (n + 1) / 2;
  for (int i = 1; i <= n; ++i) {
    scanf("%d", &a[i]);
    if (a[i]) {
      if (a[i] & 1) --cnt;
    }
  }
  memset(dp, INF, sizeof(dp));
  dp[0][0][0] = 0;
  dp[0][0][1] = 0;
  for (int i = 1; i <= n; ++i) {
    if (a[i]) {
      int t = a[i] & 1;
      for (int j = 0; j <= min(cnt, i - 1); ++j)
        dp[i][j][t] = min(dp[i - 1][j][t], dp[i - 1][j][1 - t] + 1);
    } else {
      for (int j = 1; j <= min(cnt, i); ++j)
        dp[i][j][1] = min(dp[i - 1][j - 1][1], dp[i - 1][j - 1][0] + 1);
      for (int j = 0; j <= min(cnt, i - 1); ++j)
        dp[i][j][0] = min(dp[i - 1][j][1] + 1, dp[i - 1][j][0]);
    }
  }
  printf("%d\n", min(dp[n][cnt][0], dp[n][cnt][1]));
}
