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[] counts = new int[10];
		StringBuilder sb = new StringBuilder();
		for (char c : arr) {
		    counts[c - '0']++;
		    if (c == '1' || c == '9') {
		        sb.append(c);
		    }
		}
		int total = counts[3] + counts[5] + counts[7];
		HashSet<Integer> set = new HashSet<>();
		for (int i = 0; i < sb.length(); i++) {
		    if (sb.charAt(i) == '9' || set.contains(i)) {
		        continue;
		    }
		    boolean flag = false;
		    for (int j = i + 1; j < sb.length(); j++) {
		        if (sb.charAt(j) == '9') {
		            flag = true;
		            set.add(j);
		            total++;
		            break;
		        }
		    }
		    if (flag) {
		        continue;
		    }
		    for (int j = i + 1; j < sb.length(); j++) {
		        if (sb.charAt(j) == '1') {
		            set.add(j);
		            total++;
		            break;
		        }
		    }
		}
		System.out.println(total);
	}
}