#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
template<typename T> inline bool chmax(T &a, T b) { return ((a < b) ? (a = b, true) : (false)); }
template<typename T> inline bool chmin(T &a, T b) { return ((a > b) ? (a = b, true) : (false)); }
#define int long long
//const int INF = (1LL << 60);
//const int MOD = 1e9 + 7;
vector<int> dx = { 0,1 };
vector<int> dy = { 1,0 };

signed main() {
    int n; cin >> n;
    string s; cin >> s;
    int b = 0;
    int e = 0;
    int sum_0 = 0;
    int sum_1 = 0;
    int ans = 0;
    /*while(b < n){
        ++e;
        if(s.at(e-1) == '0'){
            ++sum_0;
        }else{
            ++sum_1;
        }
        if(e-b >= 2 && sum_0 > sum_1){

        } 
        if(s.at())
    }*/
    for(int i = 0; i < n-2; ++i){
        if(s.at(i) == '0' && s.at(i+1) == '0' && s.at(i+2) == '0'){
            s.at(i+2) = '1';
            ++ans;
        }
    }
    for(int i = 0; i < n-1; ++i){
        if(s.at(i) == '0' && s.at(i+1) == '0'){
            s.at(i+1) = '1';
            ++ans;
        }
    }
    cout << ans << endl;
}