#include <bits/stdc++.h>
using namespace std;
long long int mod = 1000000007;
void __print(long long int x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(char x) { cerr << '\'' << x << '\''; }
void __print(const char *x) { cerr << '\"' << x << '\"'; }
void __print(const string &x) { cerr << '\"' << x << '\"'; }
void __print(bool x) { cerr << (x ? "true" : "false"); }
template <typename Th, typename V>
void __print(const pair<Th, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename Th>
void __print(const Th &x) {
  long long int f = 0;
  cerr << '{';
  for (auto &i : x) cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\n"; }
template <typename Th, typename... V>
void _print(Th t, V... v) {
  __print(t);
  if (sizeof...(v)) cerr << ", ";
  _print(v...);
}
void binary_rock() {
  long long int n;
  cin >> n;
  long long int i, j, k, l;
  long long int ans = 0;
  long long int sum = 0;
  string a;
  cin >> a;
  for (i = 0; i < n; i++) {
    if (i % 2 == 0) {
      if (a[i] == '0') {
        ans++;
      } else {
        sum++;
      }
    } else {
      if (a[i] == '0') {
        sum++;
      } else {
        ans++;
      }
    }
  }
  cout << min(sum, ans) << endl;
}
signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  clock_t t1 = clock();
  long long int t = 1;
  while (t--) {
    binary_rock();
  }
  clock_t t2 = clock();
  return 0;
}
