/* -*- coding: utf-8 -*-
 *
 * 3114.cc:  No.3114 0竊・ - yukicoder
 */

#include<cstdio>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 200000;

/* typedef */

/* global variables */

char s[MAX_N + 4];

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d%s", &n, s);

  int cnt = 0, on = 2;
  for (int i = 0; i < n; i++) {
    if (s[i] == '0') {
      if (on <= 1) cnt++, s[i] = '1', on++;
      else on = 0;
    }
    else on++;
  }

  printf("%d\n", cnt);
  //puts(s);

  return 0;
}