#include <cstdio>
#include <iostream>
#include <fstream>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <sstream>
#include <iomanip>
#include <cmath>
#include <cstdlib>
#include <ctype.h>
#include <cstring>
#include <string>
#include <ctime>
#include <cassert>
#include <utility>

using namespace std;

int n;
string v;

int main() {
//	freopen("date.in", "r", stdin);
//	freopen("date.out","w", stdout);

	cin >> n;

    int cnt = 0;
	v = "";
	char c = ' ';
    while(cnt < n) {
        cin >> c;
        v += c;
        cnt++;
    }

	int res = 0;
	for(int i = 1; i < n; i++) {
        if(v[i] == v[i - 1] && v[i - 1] == '1') {
            res++;
            v[i] = 0;
        }
	}

	cout << res << endl;

	return 0;
}