#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  int ans = 0;
  for (int i = 0; i < n; i++)
    if (s[i] - '0' == i % 2) ans++;
  cout << min(n - ans, ans) << endl;
  return 0;
}
