#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

const ll INF = 1e18;
void solve() {
  ll n;
  string s;
  cin >> n >> s;
  vector dp(2, vector<ll>(2, INF));
  dp[1][1] = 0;
  rep(i, n) {
    vector nex(2, vector<ll>(2, INF));
    rep(pj, 2) rep(pk, 2) rep(nk, 2) {
      if (pj == 0 && pk == 0)
        continue;
      if ((pj == 0 || pk == 0) && nk == 0)
        continue;
      nex[pk][nk] = min(nex[pk][nk], dp[pj][pk] + (s[i] - '0' != nk));
    }
    swap(dp, nex);
  }
  ll ans = INF;
  rep(j, 2) rep(k, 2) ans = min(ans, dp[j][k]);
  cout << ans << '\n';
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}