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

#define rep(i,a) for(int i=0;i<a;i++)
#define f(i,a,b) for(int i=a;i<=b;i++)
#define rf(i,a,b) for(int i=a;i>=b;i--)

using ll = long long;
using ld = long double;
using vi= vector<int>;
using vvi= vector<vi>;
using vs= vector<string>;
using pii= pair<int, int>;
using vpii= vector<pii>;
#define endl '\n'

int main(void){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
	int n;
	string s;
	
	int ans,ans1=0, ans2=0;
	
	cin >> n >> s;
	string s2=s;
	if(n==1){
		if(s[0]=='0')ans=1;
	}else if(n==2){
		if(s[0]=='1' && s[1]=='0')ans=1;
	}else{
		f(i,0,n-3){
			if(s[i]=='0'){
				if(s[i+1]=='0'){
					s[i+1]='1';
					ans1++;
				}if(s[i+2]=='0'){
					s[i+2]='1';
					ans1++;
				}
			}
		}
		rf(i,n-1,2){
			if(s2[i]=='0'){
				if(s2[i-1]=='0'){
					s2[i-1]='1';
					ans2++;
				}if(s2[i-2]=='0'){
					s2[i-2]='1';
					ans2++;
				}
			}
		}
	}
	cout << min(ans1,ans2) << endl;
}