#include<bits/stdc++.h>
using namespace std;
int N,i,n,b,c;
int main() { 
	cin>>N;
	c=N+1;
	string a;
	for ( i=0;i<N;i++ ) cin>>a[i];
	for ( i=1,n=1;i<N;i++ ) {
	for ( int j=0,b=0;j<i;j++ ) {
		if ( a[i]==a[j] ) {
			b=1;
		} 
	}	
		if ( b==0 ) n++; 
	}
	printf("%d\n",n);
}