#include <bits/stdc++.h>
using namespace std;
int main(void){
    int n;
    int count = 0;
    string s;

    cin >> n >> s;
    
    for(int i = 0; i < n; i++){
        for(int t = i + 1; t < n; t++){
            if(s.at(i) != s.at(t))continue;
            
            for(int a = i + 1; a < t; a++){
                if(s.at(a) == s.at(i))continue; 
                
                for(int b = t + 1; b < s.size(); b++){
                    if(s.at(a) == s.at(b) || s.at(b) == s.at(i))continue;
                    
                    for(int c = b + 1; c < s.size(); c++){
                        if(s.at(c) != s.at(b) && s.at(c) != s.at(a) && s.at(c) != s.at(i))count++;
                    }
                }
            }
        }
    }

    cout << count << endl;


    
    return 0;
}