#ifndef MAIN
#define MAIN
#include __FILE__

//using mint = modint998244353;

void _main(){
  cint(n);
  cstr(s);
  vector<vector<int>> v(n+1, vector<int>(3, inf)); // 1 streak
  v[0][0] = v[0][1] = v[0][2] = 0;
  rep(i, n) {
    rep(j, 3) {
      if (s[i] == '1') {
        v[i+1][0] = v[i+1][1] = *min_element(all(v[i]));
        v[i+1][2] = min(v[i][1], v[i][2]);
      }
      else {
        v[i+1][0] = v[i][2];
        v[i+1][1] = *min_element(all(v[i])) + 1;
        v[i+1][2] = min(v[i][1], v[i][2]) + 1;
      }
      //cerr << v[i+1][j] << ' ';
    }
    //cerr << endl;
  }
  cout << *min_element(all(v[n])) << endl;
}

#else
#define MAIN

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

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using strvec = vector<string>;

constexpr ll mod10 = 1000000007;
constexpr ll mod9 = 998244353;
constexpr ll inf = 10000000000000000;

#define int ll
#define double ld
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repf(i, s, n) for (int i = s; i < (int)(n); i++)
template <class... Args>
void __y_input(Args &...arg)
{
    (cin >> ... >> arg);
}

template <class... Args>
void __y_input_vec_1(int p, Args &...args)
{
    (cin >> ... >> args[p]);
}
template <class Arg>
void __y_input_vec_resize(int size, Arg &arg)
{
    arg.resize(size);
}
template <class... Args>
void __y_input_vec(int n, Args &...args)
{
    (__y_input_vec_resize(n, args), ...);
    rep(i, n)
    {
        (__y_input_vec_1(i, args), ...);
    }
}
#define cint(...)  \
    int __VA_ARGS__; \
    __y_input(__VA_ARGS__)

#define cdbl(...)     \
    double __VA_ARGS__; \
    __y_input(__VA_ARGS__)

#define cstr(...)     \
    string __VA_ARGS__; \
    __y_input(__VA_ARGS__)

#define cvec(n, ...)       \
    vector<int> __VA_ARGS__; \
    __y_input_vec(n, __VA_ARGS__)

#define cvect(t, n, ...) \
    vector<t> __VA_ARGS__; \
    __y_input_vec(n, __VA_ARGS__)

#define last cout << endl
#define yn(bl) (bl ? "Yes" : "No")
#define all(v) v.begin(), v.end()
#define acc(v) accumulate(v.begin(), v.end(), 0LL)
#define nxp(v) next_permutation(v.begin(), v.end())
ostream &yesno(bool bl)
{
    cout << yn(bl);
    return cout;
}
void cyn(bool bl){
    cout << (bl ? "Yes" : "No") << endl;
}
typedef array<int, 2> xy;
typedef array<int, 3> xyz;

template <typename T>
inline void sort(T &vec)
{
    return sort(vec.begin(), vec.end());
}
template <typename T>
inline void rsort(T &vec)
{
    return sort(vec.rbegin(), vec.rend());
}
void _main();

template <typename T>
void prefix_sum(vector<T>& p, vector<T>& s){
  s.emplace_back(p[0]);
  for (size_t i = 1; i < p.size(); i++){
    s.emplace_back(p[i] + s.back());
  }
  return;
}

template <typename T>
void compress(T a, T b){
  vector m(a, b);
  sort(all(m));
  m.erase(unique(all(m)), m.end());
  for (auto itr = a; itr != b; itr++){
    *itr = (lower_bound(all(m), *itr) - m.begin());
  }
}

template <typename T>
using rpq = priority_queue<T, vector<T>, greater<T>>;

template <class T>
void operator+=(vector<T>& v, const T t) {
  v.emplace_back(t);
}

signed main()
{
    cin.tie(0);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(15);
    _main();
    return 0;
}

#endif