#include <bits/stdc++.h>
using namespace std;

const int INF = 1 << 30;
int dp[200010][2][2];

int main() {
	int N;
	cin >> N;
	string S;
	cin >> S;
	
	for(int i = 0; i <= N; i++) {
		for(int j = 0; j < 2; j++) {
			for(int k = 0; k < 2; k++) {
				dp[i][j][k] = INF;
			}
		}
	}
	// 110,101,011,111
	dp[0][1][1] = 0;
	for(int i = 0; i < N; i++) {
		int num = S[i] - '0';
		for(int j = 0; j < 2; j++) {
			for(int k = 0; k < 2; k++) {
				if(dp[i][j][k] == INF) continue;
				for(int n = 0; n < 2; n++) {
					if(num == 1 and n == 0) continue;
					if((n == 1 and j == 1 and k == 0) or (n == 1 and j == 0 and k == 1) or (n == 0 and j == 1 and k == 1) or (n == 1 and j == 1 and k == 1)) {
						dp[i + 1][n][j] = min(dp[i + 1][n][j], dp[i][j][k] + (num != n));
					}
				}
			}
		}
	}
	cout << min({dp[N][1][1], dp[N][1][0], dp[N][0][1]}) << endl;
}