import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.regex.*;

public class Solution {

    // Complete the beautifulBinaryString function below.
    static int beautifulBinaryString(String b) {
        char[] c = b.toCharArray();
        int count = 0;
        for(int i=0;i<c.length-2;i++){
            char a = c[i];
            char d = c[i+1];
            if(a=='0' && d=='1'){
                if(c[i+2]=='0') {
                    c[i+2]='1';
                    count++;
                }
            }
        }
        return count;
    }

    private static final Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) throws IOException {
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        int n = scanner.nextInt();
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

        String b = scanner.nextLine();

        int result = beautifulBinaryString(b);

        bufferedWriter.write(String.valueOf(result));
        bufferedWriter.newLine();

        bufferedWriter.close();

        scanner.close();
    }
}

add BeautifulBinaryString.java