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

int n,dp[200001][2][2];
string s;
int main(){
	cin >> n >> s;
	for(int i = 0; i <= n; i++){
		for(int j = 0; j < 4; j++){
			dp[i][j / 2][j % 2] = 1e9;
		}
	}
	dp[0][1][1] = 0;
	for(int i = 0; i < n; i++){
		int now = s[i] - '0';
		for(int j = 0; j < 4; j++){
			dp[i + 1][j % 2][1] = min(dp[i + 1][j % 2][1],dp[i][j / 2][j % 2] + 1 - now);
		}
		if(now == 0) dp[i + 1][1][0] = min(dp[i + 1][1][0],dp[i][1][1]);
	}
	cout << min(dp[n][0][1],min(dp[n][1][0],dp[n][1][1]));
}