#include<iostream>
#include<iomanip>
#include<vector>
#include<math.h>
#include<algorithm>
#include<map>
#include<queue>
#include<stack>
#include<deque>
#include<set>
#include<cmath>
#include<ctime>
#include<bitset>
#define rep(i,a,b) for(int i=a;i<=b;i++)
using namespace std;
using ll = long long;
using vec = vector<ll>;
using Graph = vector<vec>;
using Pair = pair<ll,ll>;

void debug1(vec v){for(auto x:v)cout << x << ' ';cout << endl;}
void debug2(vector<Pair> v){for(auto x:v)cout << '(' << x.first << ',' << x.second << ')' << endl;}
void debug3(Graph v){rep(i,0,v.size()-1)debug1(v[i]);cout << endl;}

int main(){
    int n;cin >> n;
    string s;cin >> s;
    s = ' ' + s;
    int ans = 0;
    if(n>1)rep(i,2,n){
        if(s[i-1] == '0' and s[i] == '0'){
            s[i] = '1'; ans++;
        }
        if(i>=3)if(s[i-2] == '0' && s[i-1] == '1' && s[i] == '0'){
            s[i] = '1';ans++;
        }
    }
    cout << ans << endl; 
}