#include <bits/stdc++.h>
using namespace std;
int n;
string a;
int f[1005][5];
int main() {
  cin >> n >> a;
  string t = "", s = "";
  char cur = '0';
  for (int i = 0; i <= n - 1; i++) {
    t += cur;
    s += '1' - cur + '0';
    cur = '1' - cur + '0';
  }
  int ans = (int)2e9;
  int res = 0, res1 = 0;
  for (int i = 0; i <= n - 1; i++) {
    if (a[i] != s[i]) res++;
    if (a[i] != t[i]) res1++;
  }
  ans = min(res1, res);
  cout << ans;
}
