#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cctype>
#include <chrono>
#include <climits>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
// #include <atcoder/dsu>

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
#define all(a) a.begin(), a.end()
using namespace std;

template <class T> inline bool chmin(T &a, T b) {
	if (a > b) {
		a = b;
		return true;
	}
	return false;
}
template <class T> inline bool chmax(T &a, T b) {
	if (a < b) {
		a = b;
		return true;
	}
	return false;
}

template <class T1, class T2>
std::ostream &operator<<(std::ostream &out, const pair<T1, T2> &A) {
	cout << "{" << A.first << "," << A.second << "}";
	return out;
}

template <class T1, class T2>
std::ostream &operator<<(std::ostream &out, const map<T1, T2> &M) {
	for (const auto &A : M) {
		cout << "{" << A.first << "," << A.second << "}";
	}
	return out;
}

template <class T1>
std::ostream &operator<<(std::ostream &out, const set<T1> &M) {
	cout << "{";
	for (const auto &A : M) {
		cout << A << ", ";
	}
	cout << "}" << endl;
	return out;
}

template <class T1>
std::ostream &operator<<(std::ostream &out, const multiset<T1> &M) {
	cout << "{";
	for (const auto &A : M) {
		cout << A << ", ";
	}
	cout << "}" << endl;
	return out;
}

template <class T>
std::ostream &operator<<(std::ostream &out, const vector<T> &A) {
	for (const T &a : A) {
		cout << a << " ";
	}
	return out;
}

void print() { cout << endl; }

template <typename Head, typename... Tail> void print(Head H, Tail... T) {
	cout << H << " ";
	print(T...);
}

template <class T> std::istream &operator>>(std::istream &in, vector<T> &A) {
	for (T &a : A) {
		std::cin >> a;
	}
	return in;
}

using ll = long long;
constexpr int INF = numeric_limits<int>::max() / 2;
constexpr ll LINF = numeric_limits<ll>::max() / 2;

void solve() {
	// ここからスタート
	int N;
	cin >> N;
	string S;
	cin >> S;
	vector<vector<int>> dp(N + 1, vector<int>(4, INF));
	dp[0][0b11] = 0;
	for (int i = 0; i < N; i++) {
		for (int j = 0; j < 4; j++) {
			// 次の文字
			for (int k = 0; k < 2; k++) {
				if (k == 0 && j != 0b11)
					continue;
				// 遷移先
				int l = k * 2 + (j / 2);
				chmin(dp[i + 1][l], dp[i][j] + (S[i] - '0' != k));
			}
		}
	}
	cout << *min_element(all(dp.back())) << endl;
}

int main(void) {
	std::cin.tie(0)->sync_with_stdio(0);
	solve();
	return 0;
}