#include <iostream>
#include <string>
#include <list>
using namespace std;

int main()
{
  for(int i = 0; i < 10; ++i) {
    string s;
    int maxDepth = 0, maxCount = 0, count = 0, n, depth = 0;
    list<bool> status;
    cin >> n >> s;
    for(int j = 0; j < s.size(); ++j) {
      if(s[j] == '0' && depth != 0) {
        if(depth > maxDepth)
          maxDepth = depth, maxCount = count;
        while(--depth && status.back())
          status.pop_back();
        status.back() = true;
        continue;
      }
      ++count, ++depth;
      status.push_back(false);
    }
    cout << maxCount << endl;
  }
}