package contest191018;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.InputMismatchException;
import java.util.List;

public class C {
	InputStream is;
	PrintWriter out;
	String INPUT = "";
	
	void solve()
	{
		int n = ni();
		char[] s = ns(n);
		// 3 7
		// 11 59 19
		// 991 9551
		
		boolean[] unused = new boolean[n];
		int ans = 0;
		LST lst = new LST(n+1);
		for(int i = n-1;i >= 0;i--) {
			if(s[i] == '9') {
				lst.set(i);
			}else if(s[i] == '5') {
				int ne = lst.next(i);
				if(ne != -1) {
					lst.unset(ne);
					ans++;
				}else {
					unused[i] = true;
				}
			}
		}
		int one = 0;
		for(int i = n-1;i >= 0;i--) {
			if(s[i] == '1') {
				int ne = lst.next(i);
				if(ne != -1) {
					lst.unset(ne);
					ans++;
				}else {
					one++;
					unused[i] = true;
				}
			}
		}
		for(int i = 0;i < n;i++) {
			if(lst.get(i)) {
				unused[i] = true;
			}
		}
		
		int par = -1;
		for(int i = 0;i < n;i++) {
			if(s[i] == '1' && unused[i]) {
				if(par == -1) {
					par = i;
				}else {
					unused[par] = false;
					unused[i] = false;
					par = -1;
					ans++;
				}
			}
		}
		out:
		for(int i = n-1;i >= 0;i--) {
			if(s[i] == '1' && unused[i]) {
				for(int j = i;j >= 0;j--) {
					if(s[j] == '5' && unused[j]) {
						for(int k = j-1;k >= 0;k--) {
							if(s[k] == '5' && unused[k]) {
								for(int l = k-1;l >= 0;l--) {
									if(s[l] == '9' && unused[l]) {
										unused[i] = unused[j] = unused[k] = unused[l] = false;
										ans++;
										break out;
									}
								}
								break out;
							}
						}
						break out;
					}
				}
				break out;
			}
		}
		
		out:
		for(int i = n-1;i >= 0;i--) {
			if(s[i] == '1' && unused[i]) {
				for(int j = i;j >= 0;j--) {
					if(s[j] == '9' && unused[j]) {
						for(int k = j-1;k >= 0;k--) {
							if(s[k] == '9' && unused[k]) {
								unused[i] = unused[j] = unused[k] = false;
								ans++;
								break out;
							}
						}
						break out;
					}
				}
				break out;
			}
		}
		
		for(char c : s) {
			if(c == '3' || c == '7') {
				ans++;
			}
		}
		out.println(ans);
	}
	
	public static class LST {
		public long[][] set;
		public int n;
//		public int size;
		
		public LST(int n) {
			this.n = n;
			int d = 1;
			for(int m = n;m > 1;m>>>=6, d++);
			
			set = new long[d][];
			for(int i = 0, m = n>>>6;i < d;i++, m>>>=6){
				set[i] = new long[m+1];
			}
//			size = 0;
		}
		
		// [0,r)
		public LST setRange(int r)
		{
			for(int i = 0;i < set.length;i++, r=r+63>>>6){
				for(int j = 0;j < r>>>6;j++){
					set[i][j] = -1L;
				}
				if((r&63) != 0)set[i][r>>>6] |= (1L<<r)-1;
			}
			return this;
		}
		
		// [0,r)
		public LST unsetRange(int r)
		{
			if(r >= 0){
				for(int i = 0;i < set.length;i++, r=r+63>>>6){
					for(int j = 0;j < r+63>>>6;j++){
						set[i][j] = 0;
					}
					if((r&63) != 0)set[i][r>>>6] &= ~((1L<<r)-1);
				}
			}
			return this;
		}
		
		public LST set(int pos)
		{
			if(pos >= 0 && pos < n){
//				if(!get(pos))size++;
				for(int i = 0;i < set.length;i++, pos>>>=6){
					set[i][pos>>>6] |= 1L<<pos;
				}
			}
			return this;
		}
		
		public LST unset(int pos)
		{
			if(pos >= 0 && pos < n){
//				if(get(pos))size--;
				for(int i = 0;i < set.length && (i == 0 || set[i-1][pos] == 0L);i++, pos>>>=6){
					set[i][pos>>>6] &= ~(1L<<pos);
				}
			}
			return this;
		}
		
		public boolean get(int pos)
		{
			return pos >= 0 && pos < n && set[0][pos>>>6]<<~pos<0;
		}
		
		public LST toggle(int pos)
		{
			return get(pos) ? unset(pos) : set(pos);
		}
		
		public int prev(int pos)
		{
			for(int i = 0;i < set.length && pos >= 0;i++, pos>>>=6, pos--){
				int pre = prev(set[i][pos>>>6], pos&63);
				if(pre != -1){
					pos = pos>>>6<<6|pre;
					while(i > 0)pos = pos<<6|63-Long.numberOfLeadingZeros(set[--i][pos]);
					return pos;
				}
			}
			return -1;
		}
		
		public int next(int pos)
		{
			for(int i = 0;i < set.length && pos>>>6 < set[i].length;i++, pos>>>=6, pos++){
				int nex = next(set[i][pos>>>6], pos&63);
				if(nex != -1){
					pos = pos>>>6<<6|nex;
					while(i > 0)pos = pos<<6|Long.numberOfTrailingZeros(set[--i][pos]);
					return pos;
				}
			}
			return -1;
		}
		
		private static int prev(long set, int n)
		{
			long h = set<<~n;
			if(h == 0L)return -1;
			return -Long.numberOfLeadingZeros(h)+n;
		}
		
		private static int next(long set, int n)
		{
			long h = set>>>n;
			if(h == 0L)return -1;
			return Long.numberOfTrailingZeros(h)+n;
		}
		
		@Override
		public String toString()
		{
			List<Integer> list = new ArrayList<Integer>();
			for(int pos = next(0);pos != -1;pos = next(pos+1)){
				list.add(pos);
			}
			return list.toString();
		}
	}

	
	void run() throws Exception
	{
		is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
		out = new PrintWriter(System.out);
		
		long s = System.currentTimeMillis();
		solve();
		out.flush();
		if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
//		Thread t = new Thread(null, null, "~", Runtime.getRuntime().maxMemory()){
//			@Override
//			public void run() {
//				long s = System.currentTimeMillis();
//				solve();
//				out.flush();
//				if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
//			}
//		};
//		t.start();
//		t.join();
	}
	
	public static void main(String[] args) throws Exception { new C().run(); }
	
	private byte[] inbuf = new byte[1024];
	public int lenbuf = 0, ptrbuf = 0;
	
	private int readByte()
	{
		if(lenbuf == -1)throw new InputMismatchException();
		if(ptrbuf >= lenbuf){
			ptrbuf = 0;
			try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); }
			if(lenbuf <= 0)return -1;
		}
		return inbuf[ptrbuf++];
	}
	
	private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
	private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }
	
	private double nd() { return Double.parseDouble(ns()); }
	private char nc() { return (char)skip(); }
	
	private String ns()
	{
		int b = skip();
		StringBuilder sb = new StringBuilder();
		while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ')
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}
	
	private char[] ns(int n)
	{
		char[] buf = new char[n];
		int b = skip(), p = 0;
		while(p < n && !(isSpaceChar(b))){
			buf[p++] = (char)b;
			b = readByte();
		}
		return n == p ? buf : Arrays.copyOf(buf, p);
	}
	
	private int[] na(int n)
	{
		int[] a = new int[n];
		for(int i = 0;i < n;i++)a[i] = ni();
		return a;
	}
	
	private long[] nal(int n)
	{
		long[] a = new long[n];
		for(int i = 0;i < n;i++)a[i] = nl();
		return a;
	}
	
	private char[][] nm(int n, int m) {
		char[][] map = new char[n][];
		for(int i = 0;i < n;i++)map[i] = ns(m);
		return map;
	}
	
	private int[][] nmi(int n, int m) {
		int[][] map = new int[n][];
		for(int i = 0;i < n;i++)map[i] = na(m);
		return map;
	}
	
	private int ni() { return (int)nl(); }
	
	private long nl()
	{
		long num = 0;
		int b;
		boolean minus = false;
		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
		if(b == '-'){
			minus = true;
			b = readByte();
		}
		
		while(true){
			if(b >= '0' && b <= '9'){
				num = num * 10 + (b - '0');
			}else{
				return minus ? -num : num;
			}
			b = readByte();
		}
	}
	
	private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); }
}