#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> PP;
// #define MOD 1000000007
#define MOD 998244353
#define INF 2305843009213693951
#define PI 3.141592653589
#define setdouble setprecision
#define REP(i,n) for(ll i=0;i<(n);++i)
#define OREP(i,n) for(ll i=1;i<=(n);++i)
#define RREP(i,n) for(ll i=(n)-1;i>=0;--i)
#define ORREP(i,n) for(ll i=(n);i>=1;--i)
#define rep(i,a,b) for(ll i=(a);i<=(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define chmin(k,m) k = min(k,m)
#define chmax(k,m) k = max(k,m)
#define GOODBYE do { cout << "-1" << endl; return 0; } while (false)
#define MM <<" "<<
#define Endl endl


int main(void){
    //cin.tie(nullptr);
    //ios::sync_with_stdio(false);

    ll N;
    cin >> N;
    string S;
    cin >> S;
    
    ll Ans = 0;
    REP(i,N){
        bool need = false;
        if(i>=1 && S[i-1]=='0' && S[i]=='0'){
            need = true;
        }
        if(i>=2 && S[i-2]=='0' && S[i-1]=='1' && S[i]=='0'){
            need = true;
        }
        if(i>=2 && S[i-2]=='1' && S[i-1]=='0' && S[i]=='0'){
            need = true;
        }

        if(need){
            S[i]='1';
            Ans++;
        }

    }
    cout << Ans << endl;
    
    return 0;
    
}