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

public class Solution {

    static int minimumNumber(int n, String password) {
        // Return the minimum number of characters to make the password strong
        int length = password.length();
        int testcase1 = 0, testcase2 = 0, testcase3 = 0, testcase4 = 0;
        for(int i = 0; i < length; i++){
            char ch = password.charAt(i);
            if(Character.isUpperCase(ch)){
                testcase1 = 1;
            }
            else if(Character.isLowerCase(ch)){
                testcase2 = 1;
            }
            else if(Character.isDigit(ch)){
                testcase3 = 1;
            }
            else{
                testcase4 = 1;
            }
        }
        int condition = testcase1 + testcase2 + testcase3 + testcase4;
        //System.out.println(testcase2);
        if(condition == 4){
            if(length < 6){
                return (6 - length);
            }
            else{
                return 0;
            }
        }
        else{
            if(length >= 6){
                return (4 - condition);
            }
            else{
               int remainingLength = 6 - length;
               int remainingCondition = 4 - condition;
               if(remainingLength <= remainingCondition){
                   return remainingCondition;
               } 
               else{
                   return remainingLength;
               } 
            }
        }
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        String password = in.next();
        int answer = minimumNumber(n, password);
        System.out.println(answer);
        in.close();
    }
}