#include <bits/stdc++.h>
int dp[105][105][2], a[105];
int min(int a, int b) { return a < b ? a : b; }
int main() {
  int i, j, k, n;
  memset(dp, 127, sizeof(dp));
  scanf("%d", &n);
  for (i = 1; i <= n; i++) scanf("%d", &a[i]);
  if (a[1] == 0 || a[1] % 2 == 1) dp[1][n / 2][1] = 0;
  if (n / 2 > 0 && (a[1] == 0 || a[1] % 2 == 0)) dp[1][n / 2 - 1][0] = 0;
  for (i = 2; i <= n; i++)
    for (j = 0; j <= n / 2; j++)
      for (k = 0; k < 2; k++) {
        if (a[i] == 0 || a[i] % 2 == 1)
          dp[i][j][1] = min(dp[i][j][1], dp[i - 1][j][k] + (k == 0));
        if (j > 0 && (a[i] == 0 || a[i] % 2 == 0))
          dp[i][j - 1][0] = min(dp[i][j - 1][0], dp[i - 1][j][k] + (k == 1));
      }
  printf("%d\n", min(dp[n][0][0], dp[n][0][1]));
  return 0;
}
