#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define f(i, x, n) for(int i = x; i < (int)(n); ++i)

char s[101];
bool ok[4];

int id(char c){
	if (c >= '0' && c <= '9')return 0;
	if (c >= 'a' && c <= 'z')return 1;
	if (c >= 'A' && c <= 'Z')return 2;
	return 3;
}

int main(){
	int n;
	scanf("%d%s", &n, s);
	f(i, 0, n)ok[id(s[i])] = true;
	int an = 0;
	f(i, 0, 4)if (!ok[i])++an;
	an = max(an, 6 - n);
	printf("%d\n", an);
}