#include <bits/stdc++.h>
using namespace std;
vector<int> v;
int a[106];
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  int cnt = 0;
  for (int i = 0; i < n; i++) {
    if (a[i] == 0) {
      if (a[i - 1] == 1 && a[i + 1] == 1) {
        cnt++;
        a[i + 1] = 2;
      }
    }
  }
  cout << cnt << endl;
  return 0;
}
