#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0; i<(int)n; i++)
#define repi(i,m,n) for(int i=(int)m; i<=(int)n; i++)
#define rrep(i,n) for(int i=(int)n-1; i>=0; i--)
#define rrepi(i,m,n) for(int i=(int)n; i>=(int)m; i--)
#define all(x) x.begin(),x.end()
template <typename T> inline bool chmin(T& a, const T& b) { return a > b ? a = b, true : false; };
template <typename T> inline bool chmax(T& a, const T& b) { return a < b ? a = b, true : false; };
template <typename T> void uniq(std::vector<T> &v){
    std::sort(v.begin(),v.end());
    v.erase(unique(v.begin(),v.end()),v.end());
}
using ll = long long;

int main(){
    int n; cin >> n;
    string s; cin >> s;

    int ans = 0;
    rep(a,30) rep(b,a) rep(c,b) rep(d,c) rep(e,d) if(s[e] == s[c] && s[e] != s[d] && s[e] != s[b] && s[e] != s[a] && s[d] != s[b] && s[d] != s[a] && s[b] != s[a]) ans++;
    cout << ans << endl;
    
    return 0;
}