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

#define all(v) v.begin(),v.end()
using ll = long long;
using ull = unsigned long long;
using lll = __int128;
using vll=vector<ll>;
using vvll = vector<vector<ll>>;
using P = pair<ll,ll>;
using vp=vector<pair<ll, ll>>;
//using mint=modint1000000007;
//using mint=modint998244353;

const ll INF=1ll<<60;
ll mod10=1e9+7;
ll mod99=998244353;
const double PI = acos(-1);

#define rep(i,n) for (ll i=0;i<n;++i)
#define per(i,n) for(ll i=n-1;i>=0;--i)
#define rep2(i,a,n) for (ll i=a;i<n;++i)
#define per2(i,a,n) for (ll i=a;i>=n;--i)

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }

bool solve(){
    ll N;cin>>N;
    string S;cin>>S;ll ans=0;
    rep(i,N-2){
        ll cnt0=0;
        rep(j,3) if(S[i+j]=='0') cnt0++;
        if(cnt0<=1) continue;
        if(cnt0==3) S[i+1]=S[i+2]='1',ans+=2;
        else{
            if(S[i+2]=='0') S[i+2]='1';
            else if(S[i+1]=='0') S[i+1]='1';
            else S[i]='0';
            ans++;
        }
    }

    cout << ans << endl;
    return 0;
}



int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll T=1;//cin>>T;
    rep(i,T) solve();
}