#include <bits/stdc++.h>
//#include "atcoder/all"

#pragma GCC target("avx2")
#pragma GCC optimize("Ofast")

using namespace std;

using i64 = long long;


void solve(){
  int n;
  cin >> n;
  string s;
  cin >> s;
  s = "11" + s + "11";
  n += 4;
  vector<vector<int>> dp(n + 1, vector<int>(3, n + 5));
  dp[0][0] = dp[0][1] = dp[0][2] = 0;
  for(int i = 0; i < n; ++i){
    if(s[i] == '0'){
      dp[i + 1][1] = min(dp[i + 1][1], dp[i][0] + 1);
      dp[i + 1][2] = min(dp[i + 1][2], dp[i][1] + 1);
      dp[i + 1][0] = min(dp[i + 1][0], dp[i][2]);
      dp[i + 1][2] = min(dp[i + 1][2], dp[i][2] + 1);
    }
    else{
      dp[i + 1][1] = min(dp[i + 1][1], dp[i][0]);
      dp[i + 1][2] = min(dp[i + 1][2], dp[i][1]);
      dp[i + 1][2] = min(dp[i + 1][2], dp[i][2]);
    }
  }
  cout << min({dp.back()[0], dp.back()[1], dp.back()[2]}) << endl;
}

signed main(){
  solve();
}