#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
#include <stdbool.h>

int minimumNumber(int n, char* password) {
    // Return the minimum number of characters to make the password strong
    int i=0,x;
    int count[4];
      for(int i=0;i<4;i++)
    	count[i]=0;
    int count1=0;
    while(i<n)
    {
        if(password[i]<91  && password[i]>64)
        {
            count[0]=1;
        }
        if(password[i]<123 && password[i]>96)
        {
            count[1]=1;
        }
        if(password[i]<58  && password[i]>47)
        {
            count[2]=1;
        }
        if((password[i]<46  && password[i]>32) || password[i]==64)
        {
            count[3]=1;
        }
        i++;
    }
    for(int i=0;i<4;i++)
    {
        if(count[i]==0)
            count1++;
            
    }
    if(n<6)
    {
        x=6-n;
        if(x==count1)
            return count1;
        else if(x<count1)
            return count1;
        else
        {
            return x;
        }
    }
    else
    {
         return count1;
    }
}

int main() {
    int n; 
    scanf("%i", &n);
    char* password = (char *)malloc(512000 * sizeof(char));
    scanf("%s", password);
    int answer = minimumNumber(n, password);
    printf("%d\n", answer);
    return 0;
}