#include <bits/stdc++.h>
using namespace std;
vector<pair<char, int>> runLength(const string &vec) {
	vector<pair<char, int>> res;
	for (const auto &p : vec) {
		if (res.size() == 0 || res.back().first != p) {
			res.push_back({p, 1});
		} else {
			res.back().second++;
		}
	}
	return res;
};
int main() {
	int n;
	cin >> n;
	string s;
	cin >> s;
	auto f = runLength(s);
	int ans = 0;
	for (auto [c, cnt] : f) {
		if (c == '0') {
			ans += cnt - 1;
		}
	}
	cout << ans << endl;
	return 0;
}