import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.PriorityQueue;
public class Main {
	public static int[] dp;
	public static void main(String[] args) throws NumberFormatException, IOException{
		ContestScanner in = new ContestScanner();
		int n = in.nextInt();
		String s = in.nextToken();
		int[] alp = new int[26];
		for(int i=0; i<n; i++){
			alp[s.charAt(i)-'a']++;
		}
		int resY = 0;
		int count = alp[25];
		if(alp[24] <= alp[23]+alp[22]+alp[21]){
			count += alp[24];
			System.out.println(count);
			return;
		}
		count += (alp[23]+alp[22]+alp[21]);
		alp[24] -= alp[23]+alp[22]+alp[21];
		if(alp[20] == 0){
			System.out.println(count+alp[24]/2);
			return;
		}
		int max = Math.min(alp[24], alp[20]);
		if(alp[24]>=alp[20]){
			alp[24] -= alp[20];
			resY = alp[24];
			alp[20] = 0;
		}else{
			alp[20] -= alp[24];
			alp[24] = 0;
		}
		int num = 0;
		for(int i=11; i<=20; i++){
			num += alp[i];
		}
		if(max <= num){
			System.out.println(count+num+resY/2);
			return;
		}
		count += num;
		max -= num;
		
		num = 0;
		max = Math.min(alp[10], max);
		if(max>=alp[10]){
			resY += max - alp[10];
			alp[10] = 0;
		}else{
			alp[10] -= max;
		}
		num += alp[9]+alp[10];
		if(max <= num){
			System.out.println(count+num+resY/2);
			return;
		}
		count += num;
		max -= num;
		
		max = Math.min(alp[8], max);
		if(max>=alp[8]){
			resY += max - alp[8];
			alp[8] = 0;
		}else{
			alp[8] -= max;
		}
		num = 0;
		for(int i=0; i<=8; i++){
			num += alp[i];
		}
		count += Math.min(max, num);
		if(max > num){
			max -= num;
			resY += max;
		}
		System.out.println(count+resY/2);
	}
}

class MyComp implements Comparator<int[]>{
	public int compare(int[] a, int[] b) {
		return a[0] - b[0];
	}
}
//
//class Reverse implements Comparator<Integer>{
//	public int compare(Integer arg0, Integer arg1) {
//		return arg1 - arg0;
//	}
//}

class Node{
	int id;
	List<Node> edge = new ArrayList<Node>();
	public Node(int id){
		this.id = id;
	}
	public void createEdge(Node node){
		edge.add(node);
	}
}

class MyMath{
	public final static double PIhalf = Math.PI/2.0;
	public static double pAngle(double x, double y){
		// ベクトル(1, 0)と(x, y)とのなす角を返す(rad:0 to 2pi)
		if(x == 0){
			if(y == 0){
				System.err.println("pAngle error: zero vector.");
				return 0;
			}else if(y < 0){
				return PIhalf*3.0;
			}else{
				return PIhalf;
			}
		}
		double rad = Math.atan(y/x);
		if(rad < 0){
			rad += Math.PI*2.0;
		}
		return rad;
	}
	public static long fact(long n){
		long res = 1;
		while(n > 0){
			res *= n--;
		}
		return res;
	}
	public static long[][] pascalT(int n){
		long[][] tri = new long[n][];
		for(int i=0; i<n; i++){
			tri[i] = new long[i+1];
			for(int j=0; j<i+1; j++){
				if(j == 0 || j == i){
					tri[i][j] = 1;
				}else{
					tri[i][j] = tri[i-1][j-1] + tri[i-1][j];
				}
			}
		}
		return tri;
	}

	// 最大公約数
	static int gcd(int a, int b){
		return b == 0 ? a : gcd(b, a % b);
	}

	// 最小公倍数
	static int lcm(int a, int b){
		return a * b / gcd(a, b);
	}
}

class ContestScanner{
	private BufferedReader reader;
	private String[] line;
	private int idx;
	public ContestScanner() throws FileNotFoundException{
		reader = new BufferedReader(new InputStreamReader(System.in));
	}

	public ContestScanner(String filename) throws FileNotFoundException{
		reader = new BufferedReader(new InputStreamReader(new FileInputStream(filename)));
	}
	
	public String nextToken() throws IOException{
		if(line == null || line.length <= idx){
			line = reader.readLine().trim().split(" ");
			idx = 0;
		}
		return line[idx++];
	}
	public long nextLong() throws IOException, NumberFormatException{
		return Long.parseLong(nextToken());
	}
	public int nextInt() throws NumberFormatException, IOException{
		return (int)nextLong();
	}
	public double nextDouble() throws NumberFormatException, IOException{
		return Double.parseDouble(nextToken());
	}
}