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

#include<atcoder/all>
using namespace atcoder;
using mint=atcoder::modint998244353;

#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

#define int long long

#define rep(i,n) for(int i=0;i<(n);i++)
#define rng(i,l,r) for(int i=(l);i<(r);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrng(i,l,r) for(int i=(r)-1;i>=(l);i--)

#define fi first
#define se second
#define all(x) (x).begin(),(x).end()

struct fast_io{fast_io(){cin.tie(nullptr)->sync_with_stdio(false);}}_;

signed main(){
	int N;cin>>N;
	string S;cin>>S;

	int ans=0;

	rep(i,N){
		if(S[i]=='1')continue;
		
		rng(j,i+1,min(N,i+3)){
			if(S[j]=='0'){
				S[j]='1';
				ans++;
			}
		}
	}

	cout<<ans<<endl;
}