import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        char[] arr = sc.next().toCharArray();
        int count = 0;
        int one = 0;
        int nine = 0;
        for (char c : arr) {
            if (c == '1') {
                one++;
            } else if (c == '9') {
                if (one > 0) {
                    count++;
                    one--;
                }
            } else {
                count++;
            }
        }
         count += one / 2;
        System.out.println(count);
    }
}