#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  constexpr int INF = 1001001001;
  int dp[2][2];
  rep(i, 2) rep(j, 2) dp[i][j] = INF;
  dp[1][1] = 0;
  rep(_, n) {
    char c;
    cin >> c;
    int x = c - '0';
    int ndp[2][2];
    rep(i, 2) rep(j, 2) ndp[i][j] = INF;
    rep(i, 2) rep(j, 2) {
      if (i + j + x >= 2) chmin(ndp[j][x], dp[i][j]);
      if (i + j + 1 >= 2) chmin(ndp[j][1], dp[i][j] + 1);
    }
    swap(dp, ndp);
  }
  int ans = INF;
  rep(i, 2) rep(j, 2) chmin(ans, dp[i][j]);
  cout << ans << '\n';
}