#include <bits/stdc++.h>
using namespace std;
long long zero = 0;
long long one = 1;
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long lcm(long long a, long long b) { return (a / gcd(a, b) * b); }
long long expo(long long x, long long y) {
  long long res = 1;
  x = x % 1000000007;
  while (y > 0) {
    if (y & 1) res = (1ll * res * x) % 1000000007;
    y = y >> 1;
    x = (1ll * x * x) % 1000000007;
  }
  return res;
}
long long ncr(long long n, long long r) {
  long long res = 1;
  if (r > n - r) r = n - r;
  for (long long i = 0; i < r; i++) {
    res *= n - i;
    res /= i + 1;
  }
  return res;
}
long long max(long long a, long long b) { return (a > b) ? a : b; }
bool prime(long long n) {
  long long i;
  for (i = 2; i <= sqrt(n); i++) {
    if (n % i == 0) return false;
  }
  return true;
}
bool sortbysec(const pair<long long, long long> &a,
               const pair<long long, long long> &b) {
  if (a.second == b.second) return a.first < b.first;
  return (a.second < b.second);
}
long long rr[] = {
    0, 1, 1, 1, 0, -1, -1, -1,
};
long long cc[] = {1, 1, 0, -1, -1, -1, 0, 1};
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  long long n;
  cin >> n;
  string s;
  cin >> s;
  if (n == 1) return cout << 0, 0;
  long long dp[2][n];
  memset(dp, 0, sizeof(dp));
  dp[0][0] = (s[0] == '0');
  dp[1][0] = (s[0] == '1');
  for (long long i = 1; i < n; i++) {
    dp[1][i] = dp[0][i - 1] + (s[i] == '1');
    dp[0][i] = dp[1][i - 1] + (s[i] == '0');
  }
  cout << min(dp[0][n - 1], dp[1][n - 1]);
}
