#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
  int n;
  cin >> n;
  string s;
  cin >> s;
  if (n == 1)
  {
    cout << 0 << endl;
    return 0;
  }
  vector<int> dp(4);
  if (s[0] == '0')
  {
    ++dp[2];
    ++dp[3];
  }
  if (s[1] == '0')
  {
    ++dp[1];
    ++dp[3];
  }
  for (int i = 2; i < n; ++i)
  {
    vector<int> ndp(4);
    ndp[1] = dp[2] + (s[i] == '0');
    ndp[2] = dp[3];
    ndp[3] = min(dp[1], dp[3]) + (s[i] == '0');
    swap(ndp, dp);
  }
  int ans = 1e9;
  for (int i = 1; i < 4; ++i) ans = min(ans, dp[i]);
  cout << ans << endl;
}