#include <bits/stdc++.h>
using namespace std;
int w[110], n, C0, C1, D[110][110][2];
int main() {
  int i, j, k, l;
  scanf("%d", &n);
  for (i = 1; i <= n; i++) {
    scanf("%d", &w[i]);
    if (i % 2 == 0)
      C0++;
    else
      C1++;
  }
  for (i = 0; i <= n; i++) {
    for (j = 0; j <= n; j++) {
      D[i][j][0] = D[i][j][1] = 1e9;
    }
  }
  D[0][0][0] = D[0][0][1] = 0;
  for (i = 1; i <= n; i++) {
    for (j = 0; j < i; j++) {
      for (k = 0; k < 2; k++) {
        int t = D[i - 1][j][k];
        if (w[i]) {
          if (w[i] % 2 == 0) {
            D[i][j + 1][0] = min(D[i][j + 1][0], t + (k != 0));
          } else {
            D[i][j][1] = min(D[i][j][1], t + (k != 1));
          }
        } else {
          for (l = 0; l < 2; l++) {
            D[i][j + 1 - l][l] = min(D[i][j + 1 - l][l], t + (k != l));
          }
        }
      }
    }
  }
  printf("%d\n", min(D[n][C0][0], D[n][C0][1]));
}
