#include<bits/stdc++.h>
typedef long long ll;
using namespace std;
void FASTCODE() {
std::ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
}
int main() {
FASTCODE();
int n;
cin >> n;
string s;
cin >> s;
int sum=0;
for(int i=0;i<n;i++){
int fre[231]={0};
for(int j=i;j<n;j++){
string x="";
x+=s[j];
if(x.size()>=3){
for(int k=0;k<x.size();k++){
fre[x[k]]++;
}
bool b=true;
for(int f=0;f<=245;f++){
if(fre[f]>1){
b=false;
break;
}
}
if(b==true){
sum++;
}
}
}
}
cout << sum;
return 0;
}
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