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

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

  if(N==1){
    cout<< 1-(S[0]-'0') <<endl;
    return 0;
  }
  if(N==2){
    cout<< 2-(S[0]-'0')-(S[1]-'0') <<endl;
  }
  int ans=0;
  for(int i=1;i<N;i++){
    if(S[i-1]=='0' && S[i] =='0'){
      S[i]='1';
      ans++;
    }
    if(i-2>=0 && S[i-2]=='0' && S[i]=='0'){
      S[i]='1';
      ans++;
    }
  }

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